The Rays said Cobb was shut down on Monday after a setback in his rehab. The Tampa Bay Times reported on Tuesday that he has a partial ligament tear. He will try to pitch through it after receiving platelet-rich plasma therapy, the paper said. If that is unsuccessful, he would need Tommy John surgery.
Cobb has been out since leaving a spring training game March 17 with a forearm strain. He resumed throwing April 24.
Cobb, 27, was 10-9 with a 2.87 ERA last season and projected to be atop the Rays rotation this season.