Castro, who earned the Astros' regular catching job as a 22-year-old rookie last season, was injured Wednesday while trying to avoid a tag by Detroit Tigers first baseman Miguel Cabrera in Lakeland. It was Castro's second game of spring training.
The original diagnosis was a sprain, but an MRI revealed a tear in Castro's right meniscus. The torn ACL was discovered late Thursday and he was operated on Friday. The typical recovery time is six months.
"He might be able to come back at some point in September, but he's such a valuable person, such a valuable player, you don't want to rush a guy like that," manager Brad Mills said. "Let him take his time. Let him get stronger. He's going to be fine. As I told Jason, he was going to have a great year this year. Now, he's going to have a great year next year."
Astros medical director Dr. David Lintner operated.
"The surgery went well," general manager Ed Wade said. "Dr. Lintner indicated that the meniscus tear was significant and actually took longer to repair than the ACL."
"We've talked about all kinds of things," Mills said, "but right now we've got these five guys in camp and they're going to work and everything is going to be considered."