Asked why Manziel was still on the team in light of the fact he had lied to the coaching staff about his most recent party video, Pettine said he was "not going there."
"When I say I'm sorry to disappoint, I'm not really," Pettine said. "But I'm just not going there today. We got a game to get ready for Monday night."
A league source confirmed to ESPN on Thursday that Manziel had lied to the coaching staff about his most recent party video.
Pettine said Friday he already had explained his thinking behind making Manziel the team's third quarterback one week after making him the starter.
He added he already had made clear that "trust and accountability" were the issues that led to Manziel's demotion.
Manziel was demoted one day after an Internet video surfaced showing him holding a champagne bottle while partying at a club in Austin, Texas, during the team's bye weekend.
On Wednesday, Pettine declined to comment on whether Manziel had admitted the video was from the bye weekend.
Friday, he declined to discuss the situation at all.
Josh McCown will start for the Browns Monday night against Baltimore.
"The decision's been made," offensive coordinator John DeFilippo said. "I support that decision 100 percent."
Pettine and DeFilippo both said they were not sure if Manziel would be active against the Ravens.