One week after being named the team's starter, Manziel has been demoted to third-string quarterback for Monday night's game against the Baltimore Ravens after social media posts surfaced this week showing Manziel allegedly partying last weekend in Texas during the team's bye week.
"We all know what happened and what got put out there, and it led to much disappointment, frustration, however you want to term it," Pettine said Tuesday evening on his weekly "The Mike Pettine Show" on the Cleveland Browns Radio Network. "It was something we felt had violated the trust that we had put in him for the bye coming out of the Pittsburgh game."
Pettine said he, offensive coordinator John DeFilippo and quarterbacks coach Kevin O'Connell had spoken with Manziel before the bye to make clear they expected he would handle himself "the right way."
"The bye week would be ... wouldn't use the word 'test,' but that's essentially what it ended up being," Pettine said.
Pettine said the same group of coaches spoke with Manziel after learning of the video posted on social media. The coach added he kept owner Jimmy Haslam and general manager Ray Farmer informed during the decision-making process but called the final decision to demote Manziel "a coaching decision."
"The GM and the owner are certainly two people I want to keep in the loop, but it was simply to inform them of what we had decided," Pettine said.
Pettine's radio show appearance reinforced a statement he released earlier in the day, in which he said he felt let down by his quarterback's behavior given his on-field growth.
"Everyone in this organization wants what is best for Johnny just like we do for every player in our locker room. I'm especially disappointed in his actions and behavior because he has been working very hard," Pettine said in the statement.
"The improvements from last year to this year have been tremendous, but he still has to consistently demonstrate that he has gained a good understanding of what it takes to be successful at the quarterback position on this level. It goes well beyond the field. We are going to continue to support him in every way possible, but at this point, we've decided it's best to go with Josh as the starter going forward."
Earlier Tuesday, Pettine had said he was "not in position yet" to say whether Manziel would start Monday night and that the team was gathering information on the incident.
"It's a little easier to handle when it's just a one-time occurrence, but when behavior repeats, not just him but with anybody, it's certainly a cause for concern," Pettine said.
He added: "You have a vision of what you want the team to look like, how you want them to handle themselves when they're out of the building. We talk a lot about it ... so when things like this happen -- and not just him, but just in general -- any team when you have incidents like that [where] a guy knows that he represents more than himself and has issues off the field, it is frustrating."
McCown (ribs) has been cleared to play, Pettine said earlier Tuesday, and is "good to go" for Monday night's game.
"He's a prisoner of his success," Browns linebacker Karlos Dansby said of Manziel, who did not speak to reporters Tuesday.
Manziel had been named the Browns' starter after he threw for 372 yards in the 30-9 loss to the Steelers on Nov. 15. When he was named the starter, Pettine talked to him about properly representing the team. Manziel told reporters before the bye week that he was "not going to do anything that's going to be a distraction to this team or be an embarrassment to the organization."
Last month, Manziel made headlines after witnesses reported him driving dangerously on an interstate highway and his girlfriend said he had gotten physical with her in the car. Manziel was questioned by police, who smelled alcohol on Manziel's breath but did not give him a field sobriety test because he showed no signs of inebriation. Just last week, the NFL announced Manziel would not face discipline for the incident.
Manziel spent 10 weeks in a treatment facility during the offseason for undisclosed reasons.
Information from ESPN.com's Pat McManamon was used in this report.