He hopes another week of practice will help him revert to his efficient MVP-like form.
The Colts' franchise quarterback acknowledged Wednesday he wasn't himself in Sunday night's season-opening loss to Chicago.
"Obviously, you don't want to tell the Bears, 'Hey, I'll be this percent before the game,' " Manning said. "But I knew I probably wouldn't be 100 percent for that game. Hopefully, I can just keep working each week and get more and more comfortable."
Even Manning, who has never missed a start in 11 NFL seasons, wasn't sure what to expect after the longest absence of his pro or college career.
He spent six weeks recuperating from mid-July surgery to remove an infected bursa sac in his left knee and missed all five of Indy's preseason games. Manning didn't begin full workouts with his teammates until last week.
Clearly, the timing was off last weekend. Manning and the receivers couldn't connect consistently on deep passes and never quite had that precision the Colts' offense is known for.
"It went somewhat like I thought it would. I thought it would take about a quarter-and-a-half or two quarters to get hit and get a little bit of a feel going," he said. "But it's disrespectful to the position and to the NFL, for how difficult it is, to think that you can not only play but not practice in the preseason and expect to be at your top level in Week 1."
Manning wasn't the only player struggling against Chicago.
Indy rushed for only 53 yards, compared with 183 for the Bears, and Chicago converted 10-of-16 third downs.
So if Indy is to avoid its first 0-2 start since Manning's rookie season in 1998, the two-time league MVP and coach Tony Dungy know improvements must come swiftly.
"It needs to be [better], and it better be because we're going to have to play a lot better and I think we will," Dungy said. "That's our goal going to work in practice, sharpening up and eliminating some of those things that were just a little bit off."
Complicating matters are the adjustments Indy must make for injuries.
Pro Bowl center Jeff Saturday returned to practice Wednesday, a little more than two weeks after injuring a ligament in his right knee. Saturday was expected to miss at least six weeks but after deciding against surgery, Dungy said there was a chance he could play against the Vikings.
If he does not play, the Colts would again be protecting Manning against a strong defense with three new starters on the line -- left guard Charlie Johnson, right guard Dan Federkeil and rookie center Jamey Richard. Johnson played at left guard for the first time last weekend, while Federkeil and Richard made their first NFL starts.
Plus, the Colts may be without Clark, who injured his right knee in the first half of Sunday's game when a Chicago player landed on his leg. Clark said Monday's MRI revealed no structural damage and that he wasn't sure whether he would play Sunday.
Clark did not practice Wednesday although Dungy said he could return to work Thursday.
If Clark can't go, the Colts would likely use three receivers, adding 2007 first-round pick Anthony Gonzalez to the lineup. The Colts have been successful with that strategy when Clark sat out in previous seasons.
"I'm definitely doing everything I can to get ready, but I can't say one way or the other," Clark said.
The injury rash has even hit the coaching staff.
Offensive line coach Howard Mudd is expected to miss two weeks after undergoing surgery this week to help ease the pain he had from an earlier knee replacement. Assistant line coach Pete Metzelaars will replace Mudd at practice this week.
But the far bigger issue for Indianapolis is Manning and how quickly it will take him and the offense to get in synch.
"It's not like I had a choice of whether I played in the preseason or not," Manning said. "It wasn't one of these, 'I'm not going to play because I want to rest my legs.' It was a pretty good accomplishment in itself the fact I was able to get out there and play."