Coleman was optioned to Omaha for the second time this season.
Manager Ned Yost indicated that he'd return to a platoon arrangement with the right-handed-hitting Valencia and the left-handed-hitting Mike Moustakas. Valencia was in the lineup on Sunday against Mariners left-hander Roenis Elias.
Before his injury, Valencia was batting .289 (11-for-38) against left-handed pitchers and .194 (6-for-31) against right-handed pitchers.
"He's probably going to face most lefties right now," Yost said.
Moustakas has batted .125 (4-for-32) against lefties and .184 (29-for-158) against righties. The third baseman has six of his eight home runs against right-handed pitching.
Coleman appeared in just one game since being recalled from his earlier trip to Omaha and was ineffective. In one inning on Tuesday at Detroit, he gave up a home run to Ian Kinsler, a walk and a single.
His departure also reduces the number of pitchers in the bullpen from eight to seven.
"We've got too many guys in the bullpen, and we wanted him to go down and continue to work on some things," Yost said. "We want him to get his two-seamer going, we want him to get his slider a little bit tighter."
Coleman had a 2.16 ERA in five relief outings for Omaha, but what Yost saw at Detroit was not encouraging.
"He had the big slurvy slider. He had a four-seam fastball. He was behind in the count." Yost said. "He said, 'Well, that's the way I pitched in Triple-A.' Yeah, because you can get guys out like that at Triple-A. It doesn't work here."
Yost also noted that Coleman's fastball has lost about two miles an hour.
In 18 appearances for Kansas City this season, Coleman had a 6.41 ERA and opponents were batting .325 against him. In 2013, Coleman had a 0.61 ERA in 27 games and held opponents to a .186 average.
"He had that last year, he's just got to get it going," Yost said. "And this bullpen was built for him to be in it. We need to get him right."
Moving a pitcher out of the bullpen also gives Yost some additional flexibility with four bench players instead of three.