"Well, I just think that he's quiet. I just think you feel it,'' Pettine elaborated, when asked how he can sense it. "The competitor that he is is one of the biggest reasons we brought him here. So if he didn't feel that way, I'd be shocked.''
Manziel has played only five snaps this season while backing up starter Brian Hoyer. Hoyer is in the final year of his contract.
Earlier this season, Hoyer beat out Manziel for the Browns starting spot. He also led Cleveland to the biggest comeback win in league history, overcoming a 25-point deficit to defeat the Titans on Oct. 5.
Pettine also said that the team would like to know how Manziel has progressed, but must stand by Hoyer as the starter.
"It's a question we need to have answered, but it can't be forced," Pettine said.
Manziel, the 2012 Heisman Trophy winner at Texas A&M, was the 22nd pick of this year's draft.
- Dan Gartland