Now we now why he was doing it, thanks to Gray Caldwell and Stuart Zaas of DenverBroncos.com.
When Manning, and tight end Julius Thomas, missed practice after injuring his ankle earlier this season, he didn't want to miss out on mental reps while his teammates practiced.
Manning wore the helmet so he could hear what plays offensive coordinator Adam Gase called.
"He heard the calls, he'd repeat them to Julius and they were kind of – it was a way for them to take two hours and stay in the game plan," Gase said.
The quarterback used the iPad to watch game film at the same time. What a multitasker.
Nobody will ever accuse Manning of not preparing hard enough, especially after seeing this photo. Even when he is rehabbing his ankle in a cold tub, he is doing everything he can to stay on top of his game.