Castro, who was placed on the disabled list on Sunday with what the team is calling right knee effusion, had the knee drained and endured a pain-killing injection on Wednesday in Houston. He hopes to be able to come off the DL next week.
"A pretty significant amount of fluid came out, and it looked like they made a pretty successful draining of it," Castro said. "I had a shot in there, and hopefully, in the next few days, it starts to really feel better and I'm able to get back to being a lot more active and get more aggressive movements and see how it feels from there."
Castro, who missed all of last season after undergoing surgery on the ACL in his right knee, was hitting .254 with two homers and 20 RBIs in 20 games.
As of now the Astros aren't considering another surgery to help repair the knee, Castro said.
"The reason why we took the route we did of draining and giving the shot is so I can try to play the rest of the year and push that back and avoid having to miss any more time," Castro said. "If that's something that comes up later, we'll deal with it then."