Wainwright, 29, was scratched from a schedule start Thursday against Colorado because of a right forearm muscle strain. He said he noticed the problem sometime ago as a result of sleeping on the arm.
He picked up his career-best 20th victory Friday in beating the Chicago Cubs. He will finish the season 20-11 with a 2.42 earned run average and 230 1/3 innings pitched.
Wainwright has struck out 213 batters, which is third in the National League. His win total, ERA and innings pitched are each second in the league.