The 36-year-old pitcher was activated from the 10-day DL after a bout with right elbow inflammation. He walked six, allowed two runs on three hits and struck out three while throwing 79 pitches Sunday.
Wainwright (1-3) said he aggravated his elbow problem on the third-to-last warm-up pitch.
"It's tough. If I'm able to go out there and make pitches and put my arm in the position where it allows me to execute, then I will take my chances against anyone,'' he said. "But I wasn't able to execute, so I was falling behind, and I didn't want to give in, so I was walking some guys."
Wainwright said he couldn't locate his fastball or throw his good cutter.
"I need to pause and get it right,'' Wainwright said. "This team deserves more than that, and the fans deserve more than that, and the organization does, too. If I'm going to be a force down the stretch, I need to get healthy first. Luckily, we have a lot of young guys primed for this position.''
Information from The Associated Press was used in this report.