Lerew, a right-hander, was called up from Double-A Northwest Arkansas to make Thursday night's start against the Red Sox. That's because Davies and his replacement, Dusty Hughes, were not ready.
Davies has not pitched since Sept. 13 in Cleveland because of soreness in the lower back part of his right shoulder. That has cast doubt that the right-hander will pitch again in the last week and a half of the season.
"I'm hoping that he will, but I don't know that's going to happen," Royals manager Trey Hillman said. "He's still experiencing some soreness, and we're being more precautionary than aggressive in that situation."
Starters Gil Meche and Brian Bannister, also right-handers, already have been ruled out for the rest of the season because of shoulder fatigue.
The shoulder problem comes at an inopportune time for Davies, who seemed to be headed for another fast finish. He won his past four starts, and his ERA in those victories was 1.57. In 2008, he went 4-1 in September.
Overall this year, Davies has an 8-9 record and a 5.27 ERA in 22 starts.
Hughes, a left-hander up from Triple-A Omaha, took Davies' spot last Saturday night in Chicago, but he left in the fifth inning with a nerve irritation in his left elbow.
"Dusty is getting better," Hillman said. "When he played catch yesterday, he felt much better, but not to the point where we're ready to throw him right back in the rotation."
Hughes could return, but to the bullpen. Therefore, if Lerew is impressive enough on Thursday night, he could get another start before the season ends.
To make room for Lerew on the 40-man roster, the Royals placed left-hander Bruce Chen on the 60-day disabled list with a torn left oblique muscle. They also activated right-handed reliever Juan Cruz from the 15-day DL.
Chen, who was 1-6 with a 5.78 ERA in 17 games (nine starts), will take four to six weeks to heal.
"Right now, it's not sore, but I can't pitch," Chen said.
No newcomer to the Majors, Lerew, 26, pitched in 11 games for the Atlanta Braves in three seasons with an 0-2 record and an 8.31 ERA. The two losses came in 2007 during his three starts for the Braves. That was his last year in the Majors.
"The [Double-A] numbers were good, and obviously, he's got a little bit of experience from his Atlanta days," Hillman said. "He's a big strong kid. ... The reports are that he's been very committed and dedicated and has pretty good stuff."
After pitching for the Braves in 2007, he underwent reconstructive elbow surgery later that summer and missed most of last season. Released by the Braves this year, he was signed by the Royals during Spring Training and had a 10-6 record and a 4.09 ERA for Northwest Arkansas plus a 2-0 mark and an 0.60 ERA in the Texas League playoffs.
"I feel good, I feel strong," Lerew said. "Everybody down there did a good job of getting me right."
Cruz will be available out of the bullpen on Thursday night. He was 3-4 with a 6.17 ERA in 43 games when he went on the disabled list on Aug. 6 with a right shoulder strain.
Meanwhile, left-handed reliever John Bale will throw a batting-practice session on Saturday to see if he can pitch in the last week. He's been out since Sept. 4 with a leg injury.
After closer Joakim Soria recorded saves in three straight games that included a five-out effort on Sunday, a perfect inning on Monday and a one-pitch appearance on Tuesday, Hillman ruled him out of Wednesday night's game against the Red Sox.
"I think it's unfair for me to ask him, so I took the monkey off his back and just told him, 'I won't use you,'" Hillman said.
The Royals have been wary of overusing Soria because of shoulder problems he had early in the season.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.