Who can't be replaced in 2010?

When Texas offensive coordinator Greg Davis saw quarterback Colt McCoy limp off the field with an injured throwing shoulder during the Citi BCS National Championship Game last season, his instant reaction was probably the same as every Longhorns fan sitting in the Rose Bowl.

"Boy, I sure wish Garrett Gilbert would have gotten more snaps this season," Davis thought to himself.

Gilbert, a freshman from Austin, was forced into action after McCoy suffered a pinched nerve in his right shoulder during the Longhorns' first drive in a 37-21 loss to Alabama. Before facing the Crimson Tide's menacing defense, Gilbert had attempted 26 passes in nine games, all of them coming during mop-up duty.

"I would have liked for Garrett to get more snaps, just like everybody else, after it happened," Davis said.

Gilbert played admirably under difficult circumstances, completing 15 of 40 passes for 186 yards with two touchdowns and four interceptions in the defeat.

But without McCoy under center, the Longhorns looked like the Rolling Stones performing without Mick Jagger or U2 playing without Bono.

It just didn't look right and didn't feel right with McCoy standing on the sideline wearing a headset, watching Gilbert trying to lead the Longhorns to a fourth-quarter comeback.

McCoy was the heart and soul of the Longhorns, the one player they couldn't live without.

A third-round choice of the Cleveland Browns in April's NFL draft, McCoy led Texas to an NCAA-record 45 victories during his four seasons as a starter and finished in the top 3 in Heisman Trophy voting after his junior and senior seasons.

In many ways, McCoy was irreplaceable, even more so because his backup last season was so inexperienced.

Over the next nine weekdays, ESPN.com and "College Football Live" will examine the irreplaceable players of the 2010 college football season. The irreplaceable players aren't necessarily the best players in the country, but they might be the most valuable. More than any other players, their health and production are paramount to their teams' chances of winning conference championships and even playing for a national title in 2010.

Without quarterback Terrelle Pryor, Ohio State might look like Oklahoma without Sam Bradford, the 2008 Heisman Trophy winner, who injured his throwing shoulder in the Sooners' 14-13 loss to BYU in the '09 opener. Bradford returned for two games before being sidelined for the rest of the season, and Oklahoma limped to an 8-5 record without him.

Without tailback Dion Lewis, Pittsburgh might look like Buffalo without James Starks last season. Starks ran for 1,333 yards with 16 touchdowns in 2008, leading the Bulls to a Mid-American Conference championship. But Starks missed all of last season with a shoulder injury, and the Bulls finished 5-7 without him.

Davis said injuries suffered by high-profile players such as Bradford and McCoy last season probably won't change the way most coaches prepare their backups.

"I think it's been that way since football started to some degree," Davis said. "When you have an experienced starter, and he's going to get the majority of your snaps, it's just hard to get the backup enough snaps. I don't see it changing. I think everybody is aware of it, but it's a tough call. You do the best you can in practice and during camp to get the backups as many snaps as you can. But it's just hard to pull the starter out of the game."

Nearly all of Gilbert's playing time last season came when the game's outcome had already been decided. He played in lopsided victories over Louisiana-Monroe, Wyoming, UTEP, Colorado, Missouri, Oklahoma State, Baylor and Kansas.

"When the game is in hand, what kind of quality reps are you going to get him?" Davis said. "If you start throwing screens and slinging the ball around, you're not being very sportsman. People think you're trying to run the score up."

And Davis said it's difficult to put an inexperienced player into a tight game because of fear he'll make a big mistake. Gilbert didn't play in narrow victories over Texas Tech, Oklahoma, Texas A&M and Nebraska.

"If you put a freshman into the Red River Rivalry, and he throws an interception, everybody's going to say, 'What were you doing?'" Davis said. "It's a tough deal. It's something we talk about. What we try to do is get them in the ballgame as quickly as we can, let them learn the offense and still try to show good sportsmanship."

Oklahoma offensive coordinator Kevin Wilson said he worries about putting reserves in the game even after the outcome is decided. If an opponent comes back to make the score less than convincing, a team could be punished in the polls, which are a component of the system to determine which teams play in the BCS championship game.

"To me, it's all about how you manage it," Wilson said. "It's a tough deal when you're playing for these rankings. If you start playing these young kids, and the game is a little closer, some voter on the West Coast who didn't watch the game might not think you played very well."

When Bradford went down against BYU last season, the Sooners had to turn to redshirt freshman Landry Jones, who hadn't taken a snap in a college game. Jones, from Artesia, N.M., ended up starting 10 games, throwing for 3,198 yards with 26 touchdowns and 14 interceptions.

In 2002, the Sooners lost quarterback Jason White to a season-ending knee injury against Alabama in the second game. Senior Nate Hybl replaced him and led Oklahoma to an improbable Big 12 championship. In 2006, Rhett Bomar was dismissed on the eve of preseason camp, and senior Paul Thompson was moved back to quarterback from wide receiver. The Sooners finished 11-3 and won the Big 12 title.

"I've always thought you've got to be able to adjust," Wilson said. "Last year, we didn't adjust as well as we have in the past. We've always lost players and picked up and moved on."

In the past, Oklahoma tried to prepare its backup quarterbacks for game action by having them simulate plays the starter was running in practice. The reserves would stand about 15 yards behind the line of scrimmage during practice and practice their drops or handoffs.

"Even after Bradford came back last season, he said it wasn't the same," Wilson said. "In some ways, it was good. But being 15 yards behind the line is not the same as being under center. You can visualize the drive on the driving range with the water on the left at Pebble Beach. But until the water is there on Sunday, it's not the same shot."

Arkansas offensive coordinator Garrick McGee said the Razorbacks have an emergency plan in place if record-setting quarterback Ryan Mallett gets injured during a game. McGee said the Hogs go into every game with a script of the first seven offensive plays. There's another script of seven plays in case backup Tyler Wilson has to replace Mallett because of injury.

"We try to plan ahead because this is a violent game and things can happen," McGee said. "You don't want to get caught without a plan."

McGee said Arkansas coach Bobby Petrino devised the insurance plan after coaching quarterbacks for the NFL's Jacksonville Jaguars during the 2001 and '02 seasons. McGee was a quality-control assistant under Petrino at the time.

"We lost guys like Tony Boselli, Leon Searcy and Fred Taylor in a couple of weeks," McGee said. "We've tried to plan ahead ever since."

McGee said Wilson takes nearly as many reps as Mallett does during practice. In seven-on-seven passing drills, Wilson typically gets 17 or 18 snaps out of 42.

"One thing we really take pride in is that all our guys are being coached and that all the players on our roster are prepared to go into a game if they have to," McGee said.

Last season showed that it's difficult to replace some players more than others.

Mark Schlabach covers college football and men's college basketball for ESPN.com. You can contact him at schlabachma@yahoo.com.