The rookie from Cuba, who slugged three homers in his first four Major League games, has been on the disabled list since May 7 with a strained muscle in his left hand.
The A's could certainly use Cespedes' bat. Oakland totes a Major League-low .210 team batting average. A's cleanup hitters have gone just 15-for-81 (.185 average) in Cespedes' absence.
Oakland skipper Bob Melvin liked what he saw from Cespedes in the slugger's rehab assignment for Triple-A Sacramento.
"He swung the bat well, drove the ball, feels good," Melvin said.
Cespedes will return on Friday, just in time to face Kansas City's hottest pitcher. Felipe Paulino has made five starts this season, and he has held opponents scoreless in three of them. The right-hander enters Friday's series opener at Kauffman Stadium at 2-1 with a 2.03 ERA.
In his most recent outing, Paulino yielded three runs in 5 2/3 innings of a 4-3 win against the Orioles.
"He battled command a little bit more than he has his last couple of starts, but had a really sharp-breaking curveball," Royals manager Ned Yost said. "He was after it and just grinding through it."
Athletics: Bartolo looking ahead to better June
Five May starts -- over which he compiled a 7.92 ERA -- raised Bartolo Colon's overall ERA to 4.52 from 2.53. Colon is scheduled to start against the Royals on Friday.
"I think he just came up against some lineups that are a little tougher to navigate, and he threw some balls over the middle of the plate," Melvin said. "He's going to throw a lot of strikes. I don't think you envision this guy coming in going 20-2. If he pitches .500, a little better than .500, and gives us innings and takes some pressure off the bullpen, and is a resource for the younger players, all those things come into play."
Colon averaged better than seven innings per outing in March and April, but just five frames per start in May.
"I think, sometimes, when you get off to a certain start like he did, you expect him to be perfect all year," Melvin said. "That's just not the case. When he gets the ball over the middle of the plate and his command's not so good on the corners, he's going to have some games where he's going to give up some runs. At this point, his overall body of work is not bad."
Brandon Inge received a scheduled day off on Wednesday, but is slated to return to the lineup at third base on Friday.
Royals: Sanchez, Betancourt progressing on rehab stints
In his first rehab start for Triple-A Omaha, Jonathan Sanchez, recovering from biceps tendinitis, allowed one run on three hits in 5 2/3 innings. He retired the first 13 Iowa batters.
"Everybody that watched him said he threw good," Yost said. "He'll probably have one more rehab start."
Infielder Yuniesky Betancourt, rehabbing from a right ankle sprain, has spent time with Omaha and Double-A Northwest Arkansas. Yost said he could return in time to play in Kansas City's series against Oakland this weekend.
The Royals took two of three from the A's in early April, despite outscoring Oakland, 7-6, in the series.