Right-hander Daryl Thompson was optioned back to Louisville. He was sent down a day after being promoted.
The 27-year-old Volquez was Cincinnati's opening day starter. But he fell to 3-2 with a 6.35 ERA in 10 starts after absorbing a 12-4 loss on May 22 at Cleveland. He was optioned the next day to Louisville, and he went 1-0 with a 1.88 ERA in two starts.
The Reds also transferred the rehab assignment of lefty Aroldis Chapman to Double-A Carolina. He's been on the disabled list since May 16 with inflammation in his left shoulder.