Doolittle has been out since being placed on the 15-day disabled list with a strained right intercostal muscle on Aug. 24.
"Tomorrow he'll be off, and we'll see where we are with him on Friday," A's manager Bob Melvin said. "Encouraging to see he feels as good as he does."
Doolittle is eligible to come off the DL on Monday. He is 1-3 with a 2.28 ERA, 80 strikeouts and 20 saves in 54 appearances this season.
- Scooby Axson