PHOENIX — Arizona Diamondbacks ace Brandon Webb has experienced a setback in his attempts to recover from shoulder problems that have sidelined him since his opening-day start.

Webb's scheduled bullpen session on Friday was canceled when the right-hander felt tightness in the shoulder while playing catch. It was supposed to be his second bullpen workout. He felt fine after his first session on Monday, when he threw all of his pitches.

The plan had been for Webb to throw to hitters if Friday's bullpen went well, then perhaps have him make a minor league start. Manager Bob Melvin said he didn't know what the next move would be now until he talked to the team doctor.

Webb went on the 15-day disabled list April 13, retroactive to April 7.