Cashner, who was activated off the 60-day DL on Monday, initially injured his right rotator cuff on April 5 and reinjured it on May 16 in a final bullpen session before getting a minor league assignment.
After another six weeks of rehabilitation, Cashner finally pitched in a professional game in Double-A Tennessee in late July.
The process of returning to the majors has been a long one for the Cubs' No. 1 draft pick in 2008. He compiled eight rehab outings, including five with three starts at Tennessee, and three starts at Triple-A Iowa. None was more than one inning.
The Cubs will use Cashner out of the bullpen the rest of the season.
Cashner told ESPNChicago.com on Wednesday that he'll go to the Arizona Fall League and make 5-6 starts before shutting it down until 2012. The Arizona Fall League starts on Oct. 4.
Cubs pitching coach Mark Riggins said Cashner will initially just throw an inning out of the bullpen. The plan is that if he does warm up, he'll go into a game or sit down for the night. There will be no second warmup.
The Cubs hope Cashner can get stretched out a bit in the fall league and compete for a rotation spot in 2012.
Cashner said on Wednesday he'll go to spring training early a few days after the Cubs Convention.