The Colts' offense, thanks to Manning and offensive coordinator Tom Moore, is a machine. But replacing its biggest part -- a 332-pound blocker who could single-handedly neutralize an opponent's best pass-rusher -- could be the team's biggest challenge since Manning took control in 1998. On Monday, the Colts opened camp with a preview of coming attractions.
Second-round choice Tony Ugoh lined up as the first-team left tackle. He didn't look bad, but the team has plenty of options, including the more-seasoned Charlie Johnson, last year's sixth-round pick who was running with the first team during the spring. On Monday, he flopped between both backup tackle spots. Right tackle Ryan Diem could also switch to the left side or the Colts could move guard Jake Scott.
Still, the most telling sign of the Colts' confidence is that they moved forward instead of retreating. Instead of keeping tight end Dallas Clark by his left hip as added protection, the Colts let Ugoh battle defensive end Dwight Freeney in team drills. When Freeney angled his body to beat the rookie, Ugoh moved his feet well and used his long arms to direct the rush upfield, away from Manning.
Naturally, the stakes are higher when the games begin. Defenses will try to flood Ugoh's side with extra blitzers. Veteran ends will use every trick to baffle him. The rookie left tackle, who was more comfortable with run blocking than pass blocking at Arkansas, faces a tough adjustment, but the offense moves on.
"Certainly, the plan is to run our base offense," Manning said. "The plan is to be aggressive down the field, trying to hit the seams, trying to hit the deep stuff. And if it's not there, then you have the tight end on the check downs."
Glenn's retirement still could be a major speed bump to an offense that looked to get Manning back to his 49-touchdown mark of 2004. Joseph Addai, last year's first-round pick, is now the starting running back and has enough experience in the offense for him to expect Edgerrin James-like numbers (1,300-1,500 rushing yards). First-round draft choice Anthony Gonzalez gives the Colts the dangerous slot receiver they haven't had since Brandon Stokley was completely healthy in 2004.
"Obviously, our whole mentality is that we are not going to change," Clark said. "I really think that's the beauty of this team. Every year we lose this guy or lose that guy and we find a way to adjust. If they want me to block, I'll block. If they want me to catch passes, I'll catch passes."
In many ways, the Colts and the Patriots have defied the odds with their longevity in the salary cap era. The Colts have been winning since 1999. The Patriots still are going strong in the seventh year of their championship run. Normally, attrition and changes catch up to a team after six or seven years.
The Colts' offense is built to adjust as long as Manning is at the helm, and he's only getting better at 31 years old. The offense survived the early leadership and strategic losses of right tackle Adam Meadows and tight end Ken Dilger, two of Manning's favorites early in his career. Diem and Clark filled the voids. James started to lose time in his final two Colts seasons because he couldn't get to the outside as fast on stretch plays, one of the most important threats in the offense because it sets up the play-action game. Addai has that mastered after only one season.
Like most great offenses, it's vital in the Colts' attack for the left tackle to single-handedly neutralize the opponent's best pass-rusher. Manning can only do so much with quick releases and three-step drops to cover for bad left tackle play. This offense is based on threats, counter threats and precision. Getting Clark into the routes is important. Clark draws double coverage away from Reggie Wayne when he gets into routes. Having him stay in on pass plays to help a left tackle would slow down the offense.
"We call it pattern integrity," Manning said. "If Reggie Wayne is 18 yards deep, 4 yards for the sideline, then you want somebody 6 yards deep inside the numbers to put that flat defender in a bind. You need to release the tight end enough to maintain pattern integrity."
But there's a comfort zone with rushing a rookie left tackle into the mix thanks to the coaching of Howard Mudd, who is in his 34th season as an offensive line coach, including the last 10 in Indianapolis. He's one of the best at taking undrafted projects and developing them into steady blockers. Jeff Saturday developed into one of the best centers in football under his watch. Former Chiefs coach Dick Vermeil didn't like it when the team released undrafted Ryan Lilja in the first month of his rookie season. Mudd turned him into a starter.
Mudd doesn't have immediate answers on how well Ugoh will adapt, but the early signs are promising. My first impression of Ugoh is that his body is still going to grow into the left tackle position. He's tall at 6-foot-5, but he doesn't have that wide base at 305 pounds, making him one of the lighter left tackles in the league and nearly 30 pounds lighter than Glenn. A year or two of weight lifting will probably add 10 more pounds of muscle, but the team is looking for productivity now.
The minute you hear Ugoh talk, though, you understand why the Colts were willing to give up next year's first-round pick to groom him as Glenn's eventual replacement. He's bright and articulate, and brains are needed for this offense, because Manning calls out so many adjustments at the line of scrimmage. It probably also helps that Ugoh comes from an Arkansas offense that required brains along with blocking skills.
"Basically, I'm trying to get the system down working with the first unit," Ugoh said. "They are basically helping me match the no-huddle calls with the number of calls I learned previously."
Ugoh said he has to readjust his run blocking style to fit the Colts' offense. The pass blocking should be challenged daily because he's going against Freeney. For what it's worth, Ugoh has long arms and quick feet that should allow him to handle quick pass-rushers.
"You have to break him in," Freeney said. "It was a shock to me that Tarik wasn't here. It was a shock to everybody. Now, you have a rookie going in there and he has to learn it fast. The best way you can get a rookie to learn fast is to get on him and really try to get after him. Now, if he does bad and misses a block, it doesn't hurt anybody."
For now, the Colts' machine stays in the forward mode.
John Clayton is a senior writer for ESPN.com.