The Browns, who list the veteran quarterback as week-to-week, confirmed the injury Friday after defensive coordinator Ray Horton disclosed the severity of what the team previous termed a "shoulder injury."
"I was probably most disappointed for Josh," Horton said of losing to Baltimore after the Browns built a 20-2 lead. "He went out there and played with a broken collarbone ... until the last throw had a chance to win. We talk about the heritage of Ronnie Lott getting a finger amputated to play the game and how precious this game is and what guys will do to play in this game. And so, for me, it was disappointing that we didn't win it for Josh."
McCown ran to the locker room after he took a hit in the first quarter but returned to play through the painful injury. It was the second time he fractured his collarbone; McCown missed five games with the injury in 2015. This time, the injury is on the left side of his body.
The 37-year-old was in the Week 2 starting lineup after Robert Griffin III was injured in Week 1 and placed on injured reserve. McCown has started games for the Chicago Bears, Tampa Bay Buccaneers and Browns the past four seasons.
McCown was sacked three times and hit eight times against Baltimore last week but said after the game there was a reason he kept getting up.
"I have a dad and an older brother who get up and go to work and sometimes they don't feel great and they go," McCown said. "They go and they grind. I have two little boys that are playing football now. They get hit and they get banged up, and I'm trying to teach them what toughness means.
"For me, it's those things and just knowing the window for me right now (is closing) and understanding that I don't want to miss snaps."