The Reds made the move in order to keep Bailey on the same pitching schedule over the three-day All-Star break, which starts on Monday.
Bailey is slotted to make a start for Louisville on Thursday. General manager Wayne Krivsky said he is also expected to throw a bullpen session on Tuesday.
"He's not going to pitch for nine days, and it's 'a wasted roster spot,'" Krivsky said on Sunday. "[The move] keeps him on his regular schedule. He's been working on some things with [pitching coach] Dick [Pole]. And it was something that was discussed even before the game [on Saturday] as a possibility. We wanted to see how the game played out, and after the game we met again and decided it was the best thing for the team."
Krivsky said the length of Bailey's stay with Louisville was yet to be determined. Unless another Red is placed on the disabled list, Bailey must stay with Louisville for at least 10 days.
Interim manager Pete Mackanin spoke with Bailey about the move and said on Sunday that the 21-year-old rookie understood the reasoning behind the move.
"He was fine. He handled it well. He understands why we're doing it," Mackanin said. "He needs to polish his skills, and this is the best thing, I think, for the team and for him."
Bailey, who made his much-anticipated Major League debut on June 8, is 2-2 with a 6.99 ERA in six starts for the Reds this season.
Infielder Pedro Lopez was recalled from Louisville to fill Bailey's spot on the 25-man roster.
Hamilton sprains wrist: Rookie outfielder Josh Hamilton's right wrist was in a cast on Sunday morning after he injured it while swinging in the on-deck circle in the first inning on Saturday.
"I've been having a little pain [in the wrist] the last week," Hamilton said. "On deck before the first at-bat [on Saturday], I was just taking some dry swings and it popped."
Hamilton said he felt sharp pain immediately.
"It's just like a rush of fire going up my pinky," he said. "It went numb, went up into my forearm. I went to the first at-bat, and it just got worse and worse. I tried to swing in my second at-bat and I couldn't swing."
Hamilton's wrist will be in a cast until Thursday, when he will be reexamined by Reds medical director Dr. Timothy Kremchek in New York, when the Reds open the second half of the season against the Mets.
Krivsky said the initial diagnosis is a sprained ligament.
"We'll check him on Thursday and see where we go from there," Krivsky said. "He'll probably hit. If he can hit, he won't have to go on the DL. If it's something worse, we'll have to put him on the DL. At this point, it doesn't look like anything more than a day-to-day thing."
Hamilton spent close to two weeks on the disabled list earlier in the year with a case of gastroenteritis. On Sunday, he voiced his frustration with the odd ways he's missed playing time this year.
"I always get hurt doing nothing," he said. "Whenever you get injured, it's doing something strange. It's never diving for a ball or running into somebody."
Hamilton was 7-for-20 with two home runs and five RBIs over the first eight games of the Reds' homestand.
Bad time for a break: Winners of four of their past five games heading into Sunday's matchup against the Diamondbacks, the Reds were in no hurry to get to the All-Star break on Monday.
"Every team I've ever been on, as soon as you're struggling a little bit and you get something going, you got the off-day," Mackanin said. "You just wish you didn't have it. It's true, we'd like to keep this momentum. I won't say, 'Unfortunately, we have the All-Star break,' because I'm staying positive and saying we're just going to pick up where we left off after the break."
With the Reds entering Sunday 35-52 and 14 games out of first place, Mackanin said he expects their fortunes to find a turn for the better in the season's second half.
"Every team has its ups and downs," he said. "Every team gets hot, every team goes through a little slump. So I think we've had all our slumps. We're due a lot of hot streaks."
More draftees sign: On Sunday the Reds announced that four more 2007 First-Year Player Draft picks have signed with the organization. The newest signees include first-round picks Todd Frazier (shortstop, Rutgers) and Kyle Lotzkar (RHP, Delta, British Columbia), second-round pick Zack Cozart (shortstop, Ole Miss) and third-round pick Scott Carroll (RHP, Missouri State).
Up next: Tuesday's All-Star Game will give the Reds three days off before they open the second half of the season with a four-game series against the Mets in New York on Thursday at 7:10 p.m. ET. Right-hander Bronson Arroyo (3-9, 4.84 ERA) is scheduled to start for the Reds opposite Mets right-hander Orlando Hernandez (4-4, 3.22 ERA).
Patrick Allegri is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.