"It was kind of interfering with my hamstring tendon based on where it was located," he said. "They drained it, and hopefully that should provide some relief. We'll see. It's just day-to-day, I guess." Castro, who missed the entire 2011 season following surgery to repair the anterior cruciate ligament in his right knee, said he fouled a ball off his knee in the first inning Monday, which aggravated the cyst.
"I think that kind of getting it taken care of and getting it drained out and tended to will solve the problem," he said. "Like I said, it's a day-to-day kind of thing. As of right now, it's feeling OK and the more time we get away from it happening [Monday] the better it feels. As the day goes on, it feels better and better."
Castro, an All-Star this season and two-time American League Player of the Week, is having a career season, hitting .282 with 18 homers and 56 RBIs. He's the latest in a string of catching injuries for the Astros.
Carlos Corporan suffered a concussion Aug. 19 when he took a foul ball of his facemask, and his replacement, Max Stassi, was hit in the head by a pitch two days later and hasn't played since because of a concussion. Corporan could return to the Astros on Monday.
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.