Smith, who hasn't competed in a race all season as he moved to the Fox Sports broadcast team, got a call Thursday afternoon while on the golf course asking if he could replace Kahne, who is skipping the race to determine the cause of his recent excessive dehydration issues that left him nauseous and having difficulty seeing last week at Darlington.
Because of rain Saturday and Sunday at Indianapolis Motor Speedway, drivers will race with no practice and no qualifying on Monday.
Smith joked maybe he would sit in the Leavine Family Racing No. 95 car and have them make some engine noises so he could prepare for the race.
"I was literally on the golf course when [the team owner] called me," Smith said. "And then I found out about the weather forecast. ... This could be fun here.
"Of all the Turn 1s that are challenging, Indy is one of the most challenging Turn 1s that we have because it is so narrow and because guys go three- or four-wide."
Smith is no stranger to the substituting role. The "super sub" has filled in for Dale Earnhardt Jr., Tony Stewart, Kurt Busch, Kyle Larson and Aric Almirola since 2012.
"Call me whatever you want to call me as long as I get to drive occasionally," Smith said.
Smith will start 27th in the Brickyard 400. Here is how they will line up for the Brickyard 400 on Monday at 2:00 PM ET:
1. Kyle Busch (Joe Gibbs Racing No. 18 Toyota): He won back-to-back Brickyards in 2015 and 2016 -- and possibly could have made it three consecutive if not for tangling with Martin Truex Jr. last year. He is 39 points up on Kevin Harvick for the regular-season title, and a 15th-place finish or better clinches that for him.
2. Kevin Harvick (Stewart-Haas Racing No. 4 Ford): The 2003 Brickyard winner has back-to-back sixth-place finishes. He'll be a threat.
3. Martin Truex Jr. (Furniture Row Racing No. 78 Toyota): Truex has just one career top-5 at Indianapolis. But if NASCAR wants a great storyline, either Truex or Daniel Suarez wins Sunday (or Monday if it rains). Truex will have to start from the rear though after failing prerace technical inspection three times.
4. Kurt Busch (Stewart-Haas Racing No. 41 Ford): Busch's lone top-5 finish at the Brickyard came in his first race -- in 2001. This is not one of his best tracks -- his average finish is 15.6.
5. Joey Logano (Team Penske No. 22 Ford): Logano has led 55 laps in the past five Brickyards and has three top-5s to show for it. Expect him to be in the mix.
6. Brad Keselowski (Team Penske No. 2 Ford): Keselowski is riding the momentum of a Darlington finish. He has led plenty of laps at Indy (99 in eight starts) but has just one top-5.
7. Kyle Larson (Chip Ganassi Racing No. 42 Chevrolet): He struggled at Indy last year (he started 25th and finished 28th) but he's traditionally strong at the track. Many wish he would run the Indy 500 someday.
8. Clint Bowyer (Stewart-Haas Racing No. 14 Ford): Bowyer definitely wishes it was Richmond for him to get momentum into the playoffs. He has just one top-15 finish at Indy in his past five starts.
9. Ryan Blaney (Team Penske No. 12 Ford): Blaney has failed to finish his past two Brickyard starts. He did already have good news this week -- Body Armour has increased its sponsorship to be a primary for at least three races next year and will be on the car Sunday.
10. Denny Hamlin (Joe Gibbs Racing No. 11 Toyota): Hamlin had three consecutive top-5 Brickyard finishes before finishing 17th last year. Maybe it's a good thing Hamlin isn't starting up front. He has started from the pole in three of his past four races and has posted finishes of 13th, eighth and 10th in those events.
11. Chase Elliott (Hendrick Motorsports No. 9 Chevrolet): He has one top-15 finish in three starts at Indianapolis. This one could be a struggle.
12. Aric Almirola (Stewart-Haas Racing No. 10 Ford): Almirola has never led a lap and has no finish better than 13th at the Brickyard. But he's in the playoffs, and that's what counts.
13. Erik Jones (Joe Gibbs Racing No. 20 Toyota): He led 10 laps but didn't finish the race a year ago. He struggled here in Xfinity with no top-20 finish in any of his three starts.
14. Jimmie Johnson (Hendrick Motorsports No. 48 Chevrolet): A four-time Brickyard winner, Johnson isn't guaranteed a spot in the playoffs. If someone outside the current top-16 win and Alex Bowman earns 20 (and possibly 19) more points than Johnson, the seven-time Cup champion would miss the playoffs. Don't expect that to happen. But no one expected Johnson to be on the bubble.
15. Alex Bowman (Hendrick Motorsports No. 88 Chevrolet): Bowman, who hasn't raced at Indy since 2015, could race his way into the playoffs with a win or earning 20 (and possibly 19) more points than 16.
16. Ricky Stenhouse Jr. (Roush Fenway Racing No. 17 Ford): Stenhouse doesn't have a top-10 in his five Brickyard starts. He probably wishes he can race the temporary IMS dirt track again, as he did Thursday night.
17. Ryan Newman (Richard Childress Racing No. 31 Chevrolet): : Newman is one of four drivers outside the top-16 who have won the Brickyard and need a win to make it into the playoffs. He has shown speed in recent weeks (qualifying top-10 in five of the past eight races). But he'll need a perfect race to make the playoffs.
18. Austin Dillon (Richard Childress Racing No. 3 Chevrolet): Dillon has two top-10s in five career Brickyard starts. He has no stress, though, just as he hasn't had stress for the entire season since winning the Daytona 500.
19. Paul Menard (Wood Brothers Racing No. 21 Ford): Menard's only Cup win came in the 2011 Brickyard 400. He's had 257 starts since then, the longest winless streak of any full-time driver.
20. Daniel Suarez (Joe Gibbs Racing No. 19 Toyota): Suarez probably has had a tough time as it is likely that Truex replaces him next year at JGR. He could end up at Leavine Family Racing, but no one would blame him for testing the waters. He was 20th in the points last year and 20th this year. Indy is a good track for him -- he was seventh in this race last year and posted a third and seventh in his two Xfinity starts. He will have to start in the rear of the field after failing prerace tech four times.
21. Jamie McMurray (Chip Ganassi Racing No. 1 Chevrolet): McMurray won the 2010 Indy 500 and is coming off a ninth-place finish at Darlington. Can he capture the magic, win and make the playoffs? He probably has the best shot of anyone.
22. William Byron (Hendrick Motorsports No. 24 Chevrolet): Byron is 1-for-1 at Indianapolis Motor Speedway as he won the Xfinity race at the track last year.
23. Chris Buescher (JTG Daugherty Racing No. 37 Chevrolet): Buescher has a 14th and a ninth in his two Brickyard starts so don't be surprised to see him flirting with a top-10.
24. AJ Allmendinger (JTG Daugherty Racing No. 47 Chevrolet): He has two top-10 finishes at Indy -- not counting his seventh-place finish in the 2013 Indianapolis 500.
25. David Ragan (Front Row Motorsports No. 38 Ford): Ragan has finished 30th or worse in four of his past five Brickyard 400s. But he sat on the pole in 2011 and started third in 2015.
26. Michael McDowell (Front Row Motorsports No. 34 Ford): McDowell seeks his first top-15 finish at the Brickyard.
27. Regan Smith (Leavine Family Racing No. 95 Chevrolet): Smith replaces Kasey Kahne, who is sitting out until he can understand what is causing him to be dehydrated to the point of being nauseated and having trouble seeing, which happened last weekend at Darlington. Smith has not turned a lap in any race car this year.
28. Bubba Wallace (Richard Petty Motorsports No. 43 Chevrolet): Wallace has a 23rd and 14th in his two Xfinity starts at the track. He has never competed in a Cup race at Indy.
29. Matt Kenseth (Roush Fenway Racing No. 6 Ford): Kenseth has finished a trio of second-place Brickyard finishes. He has five top-5s in his past seven Brickyard starts. Glory days.
30. Ty Dillon (Germain Racing No. 13 Chevrolet): Dillon won an Xfinity race at the track in 2014. He finished 19th in this race a year ago. A 19th on Sunday would probably make him smile.
31. Matt DiBenedetto (Go Fas Racing No. 32 Ford): One of DiBenedetto's career highlights was an eighth-place finish at the Brickyard last year. He announced Friday that he won't be back in the car next season.
32. Ross Chastain (Premium Motorsports No. 15 Chevrolet): Chastain probably is looking more forward to racing an Xfinity car for Ganassi again next week than he is the Brickyard 400. But the learning experience will be important Sunday.
33. Cole Whitt (TriStar Motorsports No. 72 Chevrolet): If this team can stay out of the bottom three among the charter teams (34th-36th), that makes the charter more valuable when it goes back to Front Row. Right now, it's seven points ahead of 34th StarCom and 13 points ahead of 35th BK Racing (now owned by Front Row)
34. Landon Cassill (StarCom Racing No. 00 Chevrolet): This team also is looking to stay out of the bottom three -- if a charter is in the bottom three for three consecutive years, NASCAR can pull the charter.
35. J.J. Yeley (BK Racing No. 23 Toyota): This will be Yeley's eighth start at the Brickyard. Make that eighth NASCAR start. He was ninth in the 1998 Indianapolis 500.
36. David Starr (Rick Ware Racing No. 51 Chevrolet): This is Starr's first Cup race of 2018.
37. Jeffrey Earnhardt (Gaunt Brothers Racing No. 96 Toyota): For the first time since the first five weeks, Earnhardt is racing in back-to-back events.
38. Reed Sorenson (Premium Motorsports No. 7 Chevrolet): Sorenson is the youngest pole winner for any Cup race at the Brickyard. When he won the 2007 pole, he was 21 years, 5 months and 24 days old.
39. Timmy Hill (Carl Long Motorsports No. 66 Toyota): This is Hill's fourth start at the Brickyard. He has been running at the finish of the previous three, including a 14th-place finish last year.
40. B.J. McLeod (Rick Ware Racing No. 52 Chevrolet): He competed in this race last year and finished 32nd.