"We're going to monitor the innings he's catching, just like anybody who comes off something, especially a catcher," Cubs manager Rick Renteria said Saturday. "He's working hard. We were out there this morning, and he was moving fine. We're aware of it, and we'll do what we can to make sure he stays healthy."
Castillo acknowledged the knee had bothered him well before he had the surgery.
"There was a time when it felt a little sore, but what can I do?" Castillo said. "I'm here to play and will try to do all I can to win a game. I don't worry about it. Sometimes you have to play with pain. You're human. You need to prepare yourself before a game and do all you can do to win the game."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.