Harrison is scheduled to return to Arlington this weekend and throw a bullpen session on Sunday. If that goes well, the Rangers could send him on a 30-day rehab assignment in the Minor Leagues.
Harrison won 32 games for the Rangers as a starter in 2011-12 but has been limited to six starts the past two seasons because of back trouble. He had fusion surgery on June 3, 2014.
Harrison is ahead of Derek Holland, who is on the disabled list with a strained muscle in his left shoulder. Holland, who hasn't pitched since April 10, began his throwing program on Thursday by playing catch for 20 throws at a distance of 60 feet.