"I think we need a lift at quarterback," Trestman said. "I think we need a spark."
Cutler will be active on Sunday and will serve as Clausen's backup. Trestman said the decision was made only with the Lions game in mind, leaving the door open for a Cutler return to the starting lineup in Week 17.
Trestman was asked why he's had success with other quarterbacks, but Cutler hasn't worked out.
"That doesn't mean that it can't work out. That's where we are now," he said. "That doesn't mean the evolutionary process of Jay's growth as a quarterback can't continue and he can't get to where we think he can be. Because every quarterback's on their own journey and some people go through these times. There's clearly evidence historically that players are 30 years old, 31 years old and haven't reached their potential and by the time they conclude their career they have.
"And right now Jay is not at a good point, he's not playing as well as he can play. I've said that starts with me, that's an accountability issue with all of us as a team and he has not done that and we have not done that and that's why we've made the decision for this moment."