Manager Terry Francona told SiriusXM's MLB Network Radio on Wednesday that Carrasco will be used out of the bullpen when he returns.
"When he comes back now, it's to help us win games,'' Francona said Thursday. "That doesn't mean we don't care about his health and his well-being because we do, but we wanted to make sure that he was ready to help us win.''
Francona said Carrasco has shown in the past that he can pitch out of the bullpen and is open to that role.
Carrasco has made three minor league appearances during his rehabilitation assignment, most recently pitching for Triple-A Toledo last Sunday when he allowed two hits and a run in an inning pitching out of relief. Overall, he has allowed two hits and a run in 3⅔ innings pitched.
He was diagnosed in June with chronic myeloid leukemia, a treatable form of cancer.
Carrasco, 32, was 4-6 with a 4.98 ERA in 12 starts before he made the announcement that he was being treated for leukemia.
The Associated Press contributed to this report.