"He's been down for a while," Cubs manager Rick Renteria said of Castillo, who was sidelined with a left rib cage strain. "He had back-to-back days [last Friday and Saturday] for the first time before he arrived with us, and then I ended up using him to pinch-hit and he caught an inning. That was one of the things I was trying to stay away from."
Castillo arrived Sunday at Wrigley Field from his rehab assignment with Triple-A Iowa, where he played back-to-back games.
"For him, it's a little like Spring Training again," Renteria said. "We have to make sure we use him wisely."
John Baker, who has been matched up with Jason Hammel, caught Edwin Jackson on Wednesday. Castillo was behind the plate Monday and Tuesday this week.
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.