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 the 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.