Ramirez felt good warming up Tuesday night, but threw a slider, felt some pain and had to stop.
"I couldn't fight through it," Ramirez said. "With everything I do to stay healthy and strong, it's baffling that it's an oblique."
The right-hander was sidelined from April 17 to June 28 with inflammation in his right shoulder, and has only pitched in 13 games this year.
"It's been a tough year -- I'm not going to lie and say it hasn't," Ramirez said.