Astros catcher Jason Castro has been diagnosed with a medial meniscus tear of the right knee. "They're going to have to see once they get in there how much damage and what they have to do," Houston manager Brad Mills said. "If they have to do more, it might be a little bit longer. We'll see." The young player underwent an MRI early Thursday morning to determine the extent of the injury, which he suffered running to first base in the seventh inning of Wednesday's game against the Tigers. Castro, the club's No. 1 pick in the 2008 First-Year Player Draft who was thrust into a starting role last year.