ARLINGTON -- Less than two weeks after sustaining an oblique injury that often leads to a prolonged rehab process, A's right-hander Bartolo Colon appears days away from returning to game action.

Colon, 39, threw a bullpen session on Saturday, and the results led manager Bob Melvin to say the veteran may assume the open rotation slot on Tuesday at home against the Red Sox. Colon is eligible to come off the disabled list that day.

"[Pitching coach] Curt [Young] said it was great, so we hold out hope that potentially he will pitch on Tuesday," Melvin said.

Colon was 6-7 with a 4.22 ERA in 15 starts for the A's before being sidelined.

"He kind of forecast this from the very beginning, 'I'm going to pitch before the break,'" Melvin said. "He was always telling me that, so hopefully that's the case."

A's plan to keep Cespedes in left field

ARLINGTON -- A seemingly misplayed ball in left field by Yoenis Cespedes that led to an A's loss Friday isn't reason to consider moving the rookie back to center field, manager Bob Melvin said Saturday.

Melvin, in fact, didn't exactly concede that the ball hit off the bat of Craig Gentry with the bases loaded and two outs in the eighth inning was even catchable, though others in the clubhouse thought otherwise. Cespedes came in on the ball before racing back and watching it fly over his head.

"As he said, he came in," Melvin said. "His first instinct was to come in. We had him a little bit shallower than we normally do in that situation, based on the fact we had the go-ahead run at second base. So I agree with the fact that maybe he doesn't get it."

After Friday's game, when asked what type of read he got on the ball, Cespedes replied, "I didn't do it the right way, but even if I read the ball well, I had no chance to catch it."

He also said, "Maybe if I played left field all the time in my life before, maybe that's not going to happen."

Cespedes is a natural center fielder and has limited experience elsewhere, though the A's felt comfortable moving him to left to accommodate Coco Crisp when he was reinstated from the disabled list at the beginning of the month.

Melvin said he has no plans of flip-flopping them again.

"I don't even want to go down that road," he said. "This is where we are right now. Anything's possible in the game, but I don't want to open this up and say the possibility is for him to go back to center field. This is the way we're going to play it.

"We do know that there's going to be a learning curve with him in left field. It's not that easy to go from center field out to left field and just feel comfortable. There's going to be some plays that may have some tougher reads, but we feel like all things considered, he's got a chance to be a nice weapon for us in there, cutting runs off at the plate and keeping guys from going second to third and certainly third to home. It'll be a work in progress, but he continues to work, and you're going to have some plays like that from time to time."

Cespedes, who was sidelined by a hamstring injury for much of the month, was back at designated hitter for Saturday's contest, and Melvin said he'll likely continue rotating him between there and left field on an every-other-day basis at least through the break.

"I'm not going to run him out four, five days in a row yet," he said. "After the break we'll probably feel more comfortable running him out there every day."