After spending most of the season at Class A Lakeland working on his control, Willis will start at the Texas Rangers next Monday night.
Willis was acquired from the Florida Marlins last December along with Miguel Cabrera, and the 2003 NL rookie of the year was bothered by a knee injury early in the season. He went 0-1 with a 10.32 ERA in four starts and one relief appearance for the Tigers.
Garcia, who hasn't pitched in the major leagues since June 2007, is to start at Texas on Sept. 17. After recovering from shoulder surgery, the 33-year-old right-hander agreed to a minor-league deal with the Tigers last month and pitched a combined five scoreless innings in two starts with Lakeland and Triple-A Toledo.