May 19, 2008 10:44 AM EST

John Smoltz felt some discomfort in his shoulder after throwing a pair of bullpen sessions on Thursday and Saturday, according to The Atlanta Journal-Constitution.

Initially Smoltz was hoping to return to the mound by the end of May, but that may not happen after this setback.

"It could be anywhere between the [late May] timetable I discussed and a lot longer," said Smoltz.

He's been on the disabled list for three weeks with inflammation in the rotator cuff of his right shoulder and in a biceps tendon, as well.

Via The Atlanta Journal-Constitution