Watching Peyton's arm strength digress over the duration of the game vs. Indy, I won't be surprised if it's his arm, not his ankle. The team wouldn't want to come out and report an arm. That's just too telling and teams are going to strategize accordingly. I'm not saying the ankle is not a problem, but I believe the arm definitely is.
Peyton is as good as there's ever been, but I won't be surprised to see both him and the Broncs looking less and less spectacular as the season wears on. He's not a kid anymore and as the weather worsens, arthritic pain in the neck is certain and that could very well effect the arm, as well. This is definitely not an old man's game and I think father time is knocking on Manning's door.