ATLANTA -- Tyler Yates doesn't remember feeling anything like the pain he felt Tuesday afternoon prior to starting the final inning of his simulated two-inning game. He did know, however, that he could not throw another pitch.

"It was like 20 pitches, fastball, slider, changeup -- it felt great," said the hard-throwing right-hander, who has been on the disabled list since May 16. "I had great location, great velocity. Just when I sat down and rested and then I tried to get back up, it was super tight, super sore. I tried to throw a couple more pitches and I just decided I couldn't do it. I had to shut it down."

Yates had already visited Birmingham, Ala., and Dr. James Andrews, leaving with a diagnosis that actually gave him reason to be upbeat.

"There's nothing structural," Yates said. "Dr. Andrews told me, 'Hey, you just have a sore ligament. Just go out there and test the waters.' I've been going out there, throwing and feeling great. I don't know if maybe we pushed it a little too fast this time, but it's very frustrating for me."

Tuesday's setback is particularly frustrating for Yates, who had already completed four mound sessions and, upon completion of Tuesday's, would have joined Triple-A Indianapolis on Friday for a rehab assignment.

"From here, I don't know what's going to go on," he said. "Of course I'm going to have to go see somebody. Probably get all the tests done again see if something happened. But that's just the way it is."

Yates was 0-2 with a 7.50 ERA in 15 appearances in 2009, but had not allowed a run in either of his past two appearances -- May 13 against St. Louis, then two days later against Colorado, covering 1 2/3 innings.

Over the course of his career, Yates has bounced back from Tommy John elbow ligament surgery in June 2002, then rotator cuff surgery, which cost him all of 2005. Since his comeback from Tommy John in 2006, Yates has gone 10-11 with a 4.66 ERA. He's appeared in 203 Major League games, and last year in 72 games with the Pirates was 6-3 with a 4.66 ERA.