Gallen is scheduled to throw a simulated game Friday, Steve Stockmar of MLB.com reports.
Gallen is being brought along slowly this spring and has yet to throw in a Cactus League game. He threw a bullpen session Wednesday, about which manager Torey Lovullo said he looked great and "everything's falling in line for him," as Gallen preps to be the club's starter Opening Day. Including Friday's sim game, the right-hander will pitch in five games this spring.