Peavy had shoulder surgery on July 14, 2010, and struggled with fatigue at times this season. The right-hander finished 7-7 with a 4.92 ERA in 111 2-3 innings.
"Hopefully a few days' rest and the off-season will help Peavy go back to what he was," Chicago manager Ozzie Guillen said. "I don't think there is any reason to go out and push something you don't have to and (make) it worse."
Peavy is looking forward to a clean slate in 2012.
"The decision's been made and I think it's a good one," he said. "Obviously, it has been a grind."
Chicago began the day second in the AL Central, 9 1/2 games behind Detroit with 18 to play.