OAKLAND -- With Yoenis Cespedes still on the mend, the A's brought in center-field help Friday by calling up Collin Cowgill, a move that led to the demotion of Michael Taylor.

Cespedes, who has missed three straight games because of a muscle strain in the back of his left hand, could potentially be back in the lineup Saturday. But nothing is guaranteed, and the A's were in need of a true center fielder, so as to allow Josh Reddick to return to familiar ground in right field.

"It's tough duty for Reddick to have to move over to center field after being in right for as long as he has," manager Bob Melvin said. "We knew we needed someone we could count on in center field, and Collin's been that guy. Certainly nothing Michael Taylor did to deserve to go down, but more just about need of a center fielder."

Cowgill, 25, was on the A's Opening Day roster but appeared in just four games before being optioned to Triple-A Sacramento on April 17 to garner more at-bats. He struggled from the get-go, hitting .179 over his first seven games before finding a groove and batting .340 over his final 12. Overall, he compiled a .387 average with runners in scoring position and tallied two home runs and 16 RBIs with four stolen bases.

Cowgill was immediately inserted into the lineup Friday, batting ninth against the Tigers.

For Taylor, the trip back to Sacramento follows a short stay in Oakland, where he collected three hits in 16 at-bats for a .188 average spanning four games. Though the numbers aren't overwhelming, Melvin said he was impressed by his at-bats.

"They were more competitive here than we've seen in the past," he said. "He seems to be playing with a lot more confidence. I know his numbers would show that he wasn't tearing the cover off the ball here, but he's had some tough assignments in his starts and did some things for us."

Carignan called up, replaces Miller in bullpen

OAKLAND -- A taxed A's bullpen received right-handed relief Friday, when the club called up Andrew Carignan and optioned Jim Miller, who was forced to throw three innings in the previous night's loss.

Oakland's relievers have combined to pitch 27 2/3 innings over the past six games, including 6 2/3 on Thursday after starter Bartolo Colon surrendered eight runs in less than three innings.

Carignan departed Triple-A with the command he didn't have at the start of the season in Oakland. He had a 6.23 ERA in five games with the A's but proceeded to put together a 1.64 mark in Sacramento, where he struck out 17 and walked just one in 11 innings.

The decision to send down Miller was based on need, not performance, manager Bob Melvin said. The right-hander fared well in six relief appearances with Oakland, pitching to the tune of a 1.93 ERA and .229 opponents batting average.

"You look at his numbers, and he's thrown the ball really well for us," Melvin said. "I think he really opened some eyes here. Looking at the pecking order out of Spring Training, I don't think we envisioned him being at the big leagues at this point in time, and now he's on the roster and has jumped ahead of some guys. He made use of his stay here, and I wouldn't be surprised if he's back soon."

The A's still have just three right-handers in the bullpen, compared to four lefties.

Sizemore rejoins A's, begins rehab process

OAKLAND -- As friend Brandon Inge settles into third base in Oakland, Scott Sizemore is doing the same in the trainer's room.

Sizemore, primed for a breakout year at third before incurring a torn ACL in his left knee on the first day of spring workouts, shed himself of his brace just last week and is working to regain strength and range of motion. Lunges, squats and walking on an inclined treadmill are among the activities on his daily to-do list.

"It feels really good to be able to do normal stuff again," Sizemore said from the A's clubhouse Friday. "All the inflammation is pretty much out of there. I feel good enough to where I could jog shortly in a couple of weeks. On paper, I'm two months away from that, but the positive comes in me feeling like I could do it now.

"I can tell, week by week, the exercises we're doing, it's getting stronger, more stable. I'm steadily improving, and that's all I can ask for."

Baseball activity, meanwhile, will have to wait. The plan is for Sizemore to be ready for batting practice by September, and by the start of the offseason, he should be able to go about a rather normal workout routine -- just as he would any other winter -- while continuing the strengthening process. Barring any setbacks, he'll no doubt be back on the field for the start of Spring Training.

For now, he's enjoying being off the couch -- "I was bored out of my mind," he said -- and back in the dugout, cheering on teammates, including Inge, who served as a mentor to Sizemore during their days together in Detroit. Both also are products of Virginia Commonwealth University, though drafted eight years apart.

"He was the veteran that took me under his wings in Detroit and showed me the ropes," Sizemore said. "Just a great guy to be around. He has a great heart, plays the game the right way and, as a teammate, he's one of the best."