I hate to resort to fat jokes, but Tarik Glenn's sudden retirement leaves an enormous hole in the Colts' offense. While it wasn't always pretty, Glenn put in a decade of life-saving pass blocking and was, for most of his career, the guy the Colts liked to run behind when they really needed yards. While he didn't get as much press, many scouts considered him almost as valuable as Manning, Marvin Harrison and Reggie Wayne. You just don't replace a guy like that very easily.
While Ugoh will almost certainly be his eventual replacement, he doesn't look ready to step in quite yet; maybe at guard, but not at the all-important left tackle position. He just has too much to learn, not the least of which is Glenn's enviable dedication to his craft.
Most casual observers would probably expect right tackle Ryan Diem to slide over, but his pass-blocking is just good enough to get by on the right side — he'd be slaughtered on the left, and so would Manning. Diem has a real problem with speed rushers, and there isn't a defensive co-ordinator in the league who wouldn't exploit it. He would, at the very least, need plenty of chipping help from a back of tight end and that would grreatly reduce the Colts' offensive effecctiveness. Or worse, it could give Jim Sorgi an extended chance behind center.
As Ed Thompson pointed out, the most likely starting candidate — at least as a stop-gap measure — is Charlie Johnson. A sixth-round pick last season (actually the second tackle they took in that draft), Johnson raised eyebrows as a rookie and fared very well in the Super Bowl after Diem went down with an ankle injury. A former tight end (like Glenn), Johnson has quick feet and good awareness, but little power and not much of a mean streak. Besides, he has no real NFL experience at left tackle, taking virtually all his snaps on the right side. Trusting Manning's precious backside to him on a play-in, play-out basis might just be too big a stretch.
The other realistic option, and this may surprise many, is starting right guard Jake Scott. While it's true that he plays at about 280 and is hardly overpowering, he is 6'5 with good footwork and long arms. He's not the guy you want there fulltime, but he could be a decent fill-in until Johnson or Ugoh shows enough to take over.
• The Colts have signed three draft picks so far — receivers Anthony Gonzalez and Roy Hall and defensive end Keyunta Dawson. At this point, I normally don't worry about the status of draft picks, because the Colts generally tend to sign their picks in bunches and have them all in camp on time or close to it. The Colts are depending on Gonzalez to take over the slot position, which is pretty much a starting role, but most of the other picks are there to learn.
The exception would appear to be at cornerback, where the Colts will need contributions from Daymeion Hughes or Michael Coe or both. The Colts weren't very strong at cornerback last year and lost both starters — Nick Harper and Jason David — to free agency. Although projected starters Marlin Jackson and Kelvin Hayden were high draft picks, neither has done much to distinguish himself, and Jackson has been nothing short of atrocious in single coverage. Nominal No. 3 Tim Jennings has all the talent in the world, but hasn't shown enough durability to be counted on. After that, it's basically the rookies, so the faster they get into camp, the better. Because, if the rooks don't get the necessary reps (or fall to an avoidable injury), you could see guys like T.J. Rushing, Antonio Perkins or even (shudder) Tanard Davis lining up against NFL wideouts.