With less than three minutes left, McNabb was hurt during the play in which he threw an interception that Roy Williams returned 46 yards for Dallas' winning touchdown.
Eagles Coach Andy Reid said McNabb underwent testing Tuesday and was waiting to see a specialist, the New York Times reported.
Asked if McNabb would play Sunday, Reid said, "I wouldn't bet on it. He doesn't look good today."
McNabb, who had been playing with a sports hernia, said he was pushed and twisted his leg.
Reid said he had not decided whether Mike McMahon or Koy Detmer would start Sunday for the Eagles, who have lost their last three games.
Without suspended wide receiver Terrell Owens and probably McNabb, the Eagles are hurting mentally and physically in last place in the NFC East, the newspaper reported.
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