"That was a tough one," Reds manager Bryan Price said of the decision.
The Reds needed to go from a nine-man bullpen back to eight to get Arroyo into the five-man rotation.
It was also determined that Cody Reed will stay in the bullpen and not get a start next week. Price had contemplated using Reed for one start vs. the Pirates to get some starters an extra day of rest.
"That will be on hold here for a little bit," Price said. "More important than anything, it's just making sure he's locked in when he gets his opportunity to take the ball as a starter. There's zero lost optimism in Cody Reed as a starting pitcher. Right now, our best team is with this current five-man rotation and the bullpen set up the way it is."
Strong outings by Finnegan and Garrett and good work from the bullpen in the season's first week made it less necessary for Reed or Robert Stephenson to get work. Reed pitched two scoreless innings Thursday vs. the Phillies but walked the first two batters in each inning before escaping the jams.
"We wanted to have everybody on the roster because our concern was if we needed a pitcher, we couldn't access a pitcher the first 10 days unless there was an injury," Price said. "We knew we were going to add Bronson. It put the ball in the court of how did Amir do? How did Rookie do? How does the bullpen look? After Amir made his start, it certainly was impressive.
"The other part is with Cody. His last couple of outings, he hasn't been sharp with his command. It just didn't seem like it was reasonable to, in turn, take a spot from somebody in the rotation, and insert him until he was really feeling like he was throwing the ball well and I feel like he's throwing the ball well."
Mark Sheldon has covered the Reds for MLB.com since 2006, and previously covered the Twins from 2001-05. Follow him on Twitter @m_sheldon and Facebook and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.