CINCINNATI -- The Reds found themselves down a fifth starter Wednesday when pitcher Eric Milton went on the 15-day disabled list with a sprained left elbow.

It immediately opened speculation over whether top pitching prospect Homer Bailey would get called up to be Milton's replacement for this Sunday's game at Los Angeles.

Milton, who is 0-4 with a 5.17 ERA in six starts, gave up four earned runs and seven hits over 5 1/3 innings and got a no-decision in Tuesday's 7-6 loss to the Astros. The left-hander said his elbow started barking early in Tuesday's game after he tried to throw a slider.

"It didn't feel too good," Milton said. "I had been struggling with the elbow all the way back to last year. Last night, I thought was something more serious and needed to be checked out."

Milton, 31, had two stints on the DL last season, including one for a sore elbow that required arthroscopic surgery on Sept. 22. Because of that, team medical director Dr. Tim Kremchek ordered an MRI exam that ultimately revealed the inflammation from a sprain.

"It was nothing serious," Reds general manager Wayne Krivsky said.

Milton, who had allowed 11 first-inning runs over his last five starts, will be shut down from throwing for 7-10 days. His fastball velocity during the past few starts had hovered mostly in the 84-86 mph range.

"It's definitely down," Milton said. "I'd like to get it taken care of and come back and get better. I'm searching for answers. It's not fun to deal with. I just want to be pain free and healthy."

Reliever Jared Burton was summoned from his rehab assignment at Triple-A Louisville and gives the beleaguered Cincinnati bullpen eight relievers for the time being. Another move is expected this weekend when the club names a starter on Sunday.

Krivsky said pitchers already on the big-league roster and at Triple-A Louisville were being considered. If it is someone already on the club, the likeliest candidate appears to be right-hander Victor Santos.

"If it's somebody from here, fine," Krivsky said. "If it's somebody from Louisville, we'll probably fly him out the night before and pitch him the next day, whoever it is."

Lefties Bobby Livingston and Phil Dumatrait and the right-handed Bailey are the leading candidates from Louisville. Livingston, who was one of the final cuts in spring camp, is 0-3 with a 3.22 ERA in seven starts and gave up five runs -- four earned -- over 6 1/3 innings in a loss on Tuesday. His next turn would fall on Sunday. Dumatrait is 4-1 with a 2.34 ERA in six starts.

Unlike Livingston or Dumatrait, Bailey is not on the Reds' 40-man roster. But no candidate would generate the same buzz as Bailey, who has been eagerly anticipated since he became the organization's first-round draft pick in 2004.

The 21-year-old Bailey, who throws fastballs in the mid- to high-90s mph, is 3-1 with a 1.83 ERA in six starts with Louisville this season. He allowed one earned run and four hits in his previous start on Monday.

"I haven't talked to the staff yet," said Krivsky when asked about Bailey. "I haven't gotten together with everybody. We'll have to wait and see. He's making good progress with his curveball and changeup. He just turned 21. He's still learning. He's right where he needs to be. He's doing fine."

Burton's back: Burton had been out since April 8 with a strained left hamstring. He had a 5.84 ERA in nine games with Double-A Chattanooga and Louisville during his rehab assignment. The 25-year-old Rule 5 Draft pick threw 17 pitches in one scoreless inning of relief Tuesday.

"They said he threw the ball really well," Krivsky said. "He's doing fine."

Burton, who struggled in his lone appearance with the Reds last month, learned from manager Rick Sweet that he was coming back just after Louisville's 11 a.m. ET game Wednesday.

"He said you're up and you're live tonight," Burton said. "I was getting antsy. I'm looking forward to getting up here and doing what I can to help the team and get the opportunity to get back out there."

More progress: In his second milestone step of the week from his Tommy John elbow reconstruction surgery rehab, reliever Eddie Guardado threw breaking pitches off of a mound Tuesday afternoon.

Of the 20 pitches he threw, 15 were breaking balls. The lefty didn't wear spikes during the session and worked at less than 100 percent. The catcher stood a step in front of home plate.

"Everything went good. It was nice and easy," Guardado said. "No pain. You feel the ball come off your fingers and you get that little snap again. That's what you look for. It's there. Everything looks good. It's another positive day."

Guardado faced hitters for the first time in live batting practice on Monday, throwing 20 fastballs. His next live BP session is slated for Friday.

Bray update: Left-handed reliever Bill Bray was scheduled to throw his second live BP session on Thursday at the club's complex in Sarasota, Fla. Bray has yet to pitch for the Reds this season because of a fractured left index finger.

Transaction: Lefty reliever Rheal Cormier cleared waivers and was released on Wednesday. Cormier was designated for assignment on April 28.

Coming up: The Reds and Astros will wrap up their four-game series at 12:35 p.m. ET on Thursday. Aaron Harang (4-1, 4.78 ERA) will start for Cincinnati, while Matt Albers (1-1, 3.32 ERA) is scheduled to pitch for Houston.