The right-hander had been scratched from his scheduled start at Tampa Bay with a rhomboid (upper back) muscle strain.
Cahill has returned to Oakland for an MRI. The A's wrap up a three-game series at Baltimore on Thursday night.
Manager Bob Melvin told reporters Thursday that he's hopeful Cahill (6-3, 3.77 ERA) can pitch on the team's next homestand, which begins Tuesday versus the Angels.
Staff ace Sean Manaea will have season-ending shoulder surgery next Wednesday and may miss most of the 2019 season as well.