Diaz (biceps) is scheduled to throw a bullpen session Saturday, Bobby Nightengale of The Cincinnati Enquirer reports.
The 25-year-old landed on the injured list last weekend with right biceps tendinitis, but he resumed playing catch Wednesday and is set to retake the mound Saturday. Diaz is eligible to return from the injured list late next week, and he may not end up missing much more than the 15-day minumum.