New York Yankees starter CC Sabathia left the team's 4-2 loss to the Toronto Blue Jays after three innings when his right knee flared up.
The left-hander could miss his next turn in the Yankees' rotation.
Sabathia (9-5) limped off the field after his knee flared up in the third and did not return. It was his shortest outing since a 2⅔-inning stint against Toronto on July 4.
"I thought he had a little bit of a limp coming off the field," manager Joe Giarardi said. "When he came off he said he was feeling it every pitch, and that's why I pulled him."
Sabathia has worn a brace on his right knee since suffering soreness late in the 2015 season. He will return to New York on Wednesday for further examination.
"It's just frustrating," Sabathia said. "It's been healthy all year. To go out today and not have it be where I want it to be is just frustrating."
The four runs Sabathia allowed Tuesday surpassed the combined three runs he had given up in his previous six road starts, according to ESPN Stats & Information research.
The left-hander, who lost consecutive starts for the first time in 2017, acknowledged his knee led to control problems against the Blue Jays.
"It's just hard for me to get over my front side and finish the pitches," he said. "When I can't do that, I don't know where the ball is going."
Information from The Associated Press was used in this report.