"We're at the point right now where we're trying to let my knee calm down a little bit so we're just trying to give it as much rest as possible before we start getting back out," Castro said. "I think going back into kind of playing and running around and stuff, I didn't have the full opportunity to get back to where it was 100 percent and not agitated at all. I think that's where we're at right now, just trying to get it back to being calmed down and built up to get back into catching."
Castro, who missed the entire 2011 season after he underwent surgery to repair the anterior cruciate ligament in his right knee, will likely have to do some squatting, such as catching in the bullpen, before getting behind the plate in a game.
"I'm not really sure when that could be," he said.
When asked if there was a chance he might not catch again this season, Castro didn't seem to think that was a realistic scenario.
"It's day to day, so it just depends on how it starts feeling," he said.
Manager Bo Porter said the last thing the Astros want to do is compromise the health of the player that is likely the team's Most Valuable Player this year.
"He will report to the trainers each and every day the degree of soreness and how he's progressed each day and play it by ear," he said.
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.