"Doing better," manager Rick Renteria said. "Took some dry swings, some tee work, some frontside with no complaints. Did some conditioning with no complaints. He's coming along."
Before being sidelined, Castillo was batting .242 with five home runs and 21 RBIs in 43 games.
John Baker has received the bulk of the playing time at catcher in Castillo's absence.
Erik Bacharach is an associate reporter for MLB.com. Teddy Cahill is a reporter for MLB.com. Follow him on Twitter at @tedcahill. This story was not subject to the approval of Major League Baseball or its clubs.