Manning's teammates say he's a competitor who will play if he's able. Carr wants to be out there just as much, and his chances of playing this weekend seemingly improved when Manning missed his second straight practice on Thursday with an injured right heel.
After practice, coach Tom Coughlin declined to predict whether Manning would be able to start his 83rd straight game, saying only that that inflammation in Manning's heel was feeling better.
A decision on whether Manning plays may not be made until Sunday.
The No. 1 overall draft pick in 2002, Carr isn't worried. He told himself that he was going to be the starter after Manning was hurt last Sunday in a win over Kansas City, and the worst that can happen is he doesn't.
"You have to prepare yourself one way or you are going to be riding a rollercoaster all week," said Carr, who last started a game in 2007 for the Carolina Panthers. He was 10 for 22 for 95 yards passing and two interceptions in a loss to New Orleans.
He came to the Giants as Manning's backup last season and has been mostly an understudy. He appeared in three games last season and two this year, all off the bench.
"I am sure he wants to play really bad, probably as bad as I want to play," Carr said of Manning. "It's the same for every competitor, every guy who wants to be on the field. Everybody gets hurt. We're down a lot of guys now and I think everyone on the side wants to be out there to help the team."
Giants offensive coordinator Kevin Gilbride has no doubts about Carr. He said the eight-year veteran knows the Giants offense, but he might not be as familiar with some of its subtleties as Manning, who has been the starting quarterback since midway through the 2004 season.
"I expect him to do well," Gilbride said. "I would be disappointed if he doesn't play well."
Gilbride said the biggest difference is that he and Manning are on the same page after working together the past six years. He said he can look at Manning and the quarterback can almost immediately sense what is wrong and go back on the field and act like a coach in the huddle, conveying Gilbride's concerns to the offense.
Carr's most extensive play with the Giants came in the final regular-season game last year. He took over in the second half against Minnesota and was 8 for 11 for 110 yards and a touchdown.
"It's got to be frustrating for a guy that started to just be on the sidelines, and now he has a chance," Gilbride said. "So I think if I was him, and what I have observed looking at him, he seems genuinely excited about this opportunity."
For the first two days of practice, Carr has gotten the chance to throw to Steve Smith and Mario Manningham, to hand off to Brandon Jacobs and to play behind a first-team offensive line that has started 36 straight games.
"It's nice to play with the toys," Carr said. "Sometimes you feel like the brother who doesn't get to play with all he cool stuff."
Carr admits he has come a long way since his rookie season with the Houston Texans, when he was sacked 76 times, an NFL record.
"It's not even close for me mentally," Carr said. "I feel like a totally different quarterback as far as what to expect, my preparations, how I go about the game is a whole lot different than then. I guess it's what you learn going through the things I have gone through, except I'm a better player."
He also has a solid offensive line, so there is no need to duck and cover after every pass.
"If my number is called I will go out there and have lot of fun," Carr said. "We have a lot of great players on this team. We are on a win streak. Guys are feeling good and I want to be a part of it. It was good to get out there and throw some ball with those guys and sweat. It kind of felt like the old days."
The difference from his days in Houston, of course, is that if Carr starts for the 4-0 Giants, he'll be expected to win.