Diaz (biceps) is expected to be activated off the 15-day injured list Friday, Bobby Nightengale of The Cincinnati Enquirer reports.
Diaz has been out since June 19 while dealing with a biceps issue, but he faced live hitters Wednesday and is now on track to return from the injured list Friday. The 25-year-old will likely work his way back into a high-leverage role in the Reds' bullpen once healthy.