McNabb sidelined with groin injury
"It's a little more pressure, it's the real thing," McMahon said of making his eighth career start. "You have to be ready. It's the situation I've been waiting for.
"I'm going to do whatever it takes to win. I haven't started in a while, but it's not about starting. It's about going out and being productive with the offense."
McNabb's status beyond this week is uncertain. He'll see a specialist Thursday.
"He's not moving around very well," coach Andy Reid said Wednesday.
McNabb said that he will definitely undergo surgery to address the sports hernia that has plagued him most of the season, but will not make a determination on the timing of an operation until after he visits with several specialists. The surgery, which will be his first ever, he stressed, could be delayed until after the season.
"I'm not in any hurry to get up under a knife," McNabb said during a news conference on Wednesday. "I think that's just kind of natural for anyone."
McNabb also termed the interception late in Monday's loss "a mistake on my part." The Eagles' star did not go into detail about the route run by rookie wide receiver Reggie Brown, or the coverage by the Cowboys, but said he was just trying to make a play.
"Obviously, it didn't turn out right," McNabb said.
McNabb re-injured his groin Monday night while trying to tackle Cowboys safety Roy Williams after he threw an interception. Williams returned the pick 46 yards for a touchdown with 2:43 left to lead Dallas to a 21-20 comeback victory over the Eagles.
McMahon nearly led Philadelphia to the winning score after coming in for the last series against Dallas. He drove the Eagles to the Cowboys 42 before David Akers missed a 60-yard field goal attempt in the final seconds.
In four seasons with Detroit, McMahon started seven games. He has a 43.8 completion percentage (138 of 314 passes for 1,745 yards) with 10 touchdown passes and 13 interceptions, but he ran for 273 yards on 46 carries. He is 1-6 as a starter.
Detmer has been McNabb's backup the last six seasons. He is the No. 2 quarterback this year only because he holds the ball on extra points and field goals.
"Nothing against Koy. I feel I have two good quarterbacks I can trust," Reid said. "Mike gives you more mobility. He knows the offense. He's efficient in the offense."
Tight end L.J. Smith played with McMahon at Rutgers. He said it won't be much of a "drop-off" catching passes from him.
"I know him. He knows my routes," Smith said. "He's mobile like Don. He has a strong arm like Don. He's not afraid to make the long throws and he's tough, too."
He threw just eight interceptions last season when he became the first player in NFL history to throw more than 30 touchdown passes (31) and fewer than 10 interceptions.
Overall, McNabb has passed for 2,507 yards, 16 TDs and has a passer rating of 85.0 this season. His troubles started off the field with the turmoil between him and receiver Terrell Owens.
McNabb feuded with Owens throughout the summer, and the two didn't speak for a prolonged period. They clicked on the field, however, with Owens catching 47 passes for 763 yards and six TDs in seven games.
McNabb hurt his chest in the season opener and has been bothered by the sports hernia since September.
Sports hernias are most common among male athletes. A diagnosis sometimes can be tricky because, unlike more common hernias, there is not always a visible bulge in the leg or groin area. And with about 18 different variations, sports hernias can range from torn muscles to frayed muscles to a weakness in the abdominal wall.
Sometimes, the symptoms masquerade as a hip joint problem, a groin pull, a strained abdominal muscle or bursitis in the hip.
"The actual hernia didn't get worse. That is there and this is part of the groin area," McNabb said. "Now that we have a problem with the groin, it has moved to that whole area."
Information from ESPN.com senior writer Len Pasquarelli, The Associated Press and SportsTicker was used in this report.
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