Latos has been trying to come back from surgery to repair torn cartilage in his left knee on Feb. 14. He felt soreness in his forearm while throwing on Friday and had an MRI a day later.
Manager Bryan Price said on Sunday that the injury is expected to heal with rest. It's a significant setback to the Reds' hopes of getting Latos back in the rotation soon. They'd originally hoped he'd be ready to pitch by the end of April.
Latos was one of eight Reds who opened the season on the disabled list, the most in the majors.