Gregg has a 10.13 ERA and 1.688 WHIP in 10 2/3 innings this season. He signed a minor-league deal this off-season and made the team out of spring training.
"He was doing everything he could to get back on top, but it just didn't happen and now he'll be on his way to the next opportunity," Reds manager Bryan Price told reporters Monday, according to the Cincinnati Enquirer.
Gregg, 36, had not pitched since May 7, when he gave up three runs in two-thirds of an inning. After the game, Reds fans started an online petition for the Reds to part ways with Gregg.
- Dan Gartland