McNabb made a brief appearance on the practice field Thursday afternoon but did not take part in any drills, after fracturing his rib on a touchdown run late in Philadelphia's 38-10 victory over the Carolina Panthers last weekend.
"Donovan is working very hard," offensive coordinator Marty Mornhinweg said. "You know Donovan, he's doing everything in his power to get back out there, make it to this game. He's played with a broken ankle, a broken sternum and all these things. Donovan is a very tough man."
If McNabb isn't available, the Eagles will go with Kevin Kolb, the team's second-round draft pick in 2007. Kolb would make his first NFL start ahead of veteran Jeff Garcia, who signed Tuesday as an emergency backup.
"If Kevin starts the game, he's our quarterback," Mornhinweg said. "It's that simple. I don't know if I can be anymore clear. I have great confidence in Kevin."
Kolb took nearly all the reps with the first team on Thursday. Garcia and Michael Vick, who is on the active roster but still must serve one more week of his league-mandated suspension, split the remaining snaps and worked with the scout team.
"I would expect him to play at a high level," Mornhinweg said of Kolb. "He doesn't lack for any confidence and that's a good thing. That's a good thing because I'm not saying he's cocky, but if you get a player that's even on the cocky side, it's a good thing to have."
Kolb has appeared in eight games in his career, including last week against Carolina. His most notable appearance came in 2008 against Baltimore, when McNabb was benched at halftime of a 10-7 game. The Ravens went on to win 36-7, with Kolb completing 10 of 23 passes for 73 yards with two interceptions, one of which was returned for a touchdown.
"Going back to the Baltimore game, he did some really good things in that game against one of the very best defenses in the league," Mornhinweg said. "We did move the football up and down the field several times and he made a couple of critical mistakes.
"Really, there were three bad plays, two critical ones. You clean those critical ones up and now you have a chance to win the game.
"Sometimes to have great success you have to have many failures and sometimes it's sort of horrific type failures and if you are strong enough mentally and you get through that then you end up having some pretty good success."
Kolb completed seven of 11 passes for 23 yards last weekend against Carolina, but still is trying to get over that disappointing game against the Ravens.
"One of the problems with Baltimore last year, not to bring that up again, I just pressed too much," Kolb said. "I tried to show everybody right now, hey I'm ready. You just press and you can't press as a quarterback. In the forefront of my mind is just relax, play smooth, let the guys who are out there make plays and we have plenty of athletes to do it."
Meanwhile, Vick told reporters Thursday following practice that he has been happy with his progress on the field.
"Where I feel right now physically, I think my body has done a good job of responding to the conditioning and the beating I put on it the last three or four weeks," Vick was quoted as saying by 950 ESPN Philadelphia. "So I'm just excited."
Other than McNabb, backup S Quintin Demps (hamstring), backup LB Joe Mays (shoulder) and starting LG Todd Herremans (foot) did not practice. Only Herremans, who is not expected back until after the bye week at the earliest, is listed out for Sunday's game.
Information from The Associated Press was used in this report.