That's the theory being floated by NFL Films guru Greg Cosell, who's seen a lack of zip in some of Manning's throws during his study of game tape.
Cosell said during his weekly Yahoo! podcast that he and ESPN analyst Ron Jaworski both reached the same conclusion independently, then received some confirmation from an outside source.
"Ron Jaworski and I were having this conversation this week," Cosell said, via PFT. "I looked at Eli on Monday; Jaws looked at Eli on Wednesday. And he made a very interesting comment. It really struck me, and I would defer to Jaws on this because I've never taken snaps in the NFL. ... It looks to him like Eli's arm is a little tired. And that he's not driving the ball at the intermediate and deeper levels the way we've come to expect. Because Eli has a strong arm."
Manning threw 318 passes in New York's first eight games, tied with Tony Romo for eighth most in the NFL.
"And we even got that sort of confirmed by someone who's a lot closer to the situation," Cosell went on. "His arm's a little bit tired right now. He's missed some throws that he would normally make."
Let's not forget this isn't Manning's first rodeo. Now in his ninth NFL season, he's never missed a game. If Manning does have a tired arm, it's probably not the first time and he's definitely not going to talk about it.
The Giants might elect to cut down on his practice reps during the week. Beyond that, expect business as usual for No. 10.
Follow Dan Hanzus on Twitter @danhanzus.