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

Webb's scheduled bullpen session 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, 33-pitch session on Tuesday.

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.