OAKLAND -- The front end of the A's bullpen received a makeover on Wednesday, the biggest move coming with the demotion of right-hander Fautino De Los Santos, who was optioned to Triple-A Sacramento.

Righty Rich Thompson, just days after being claimed off waivers from the Angels, was designated for assignment, and another righty, Jim Miller, was selected from Sacramento to round out the flurry of roster moves.

De Los Santos, whose roster spot was taken by Wednesday's starter Jarrod Parker, compiled a respectable 3.00 ERA in six relief appearances, having not allowed a run in five of his six games. But his other numbers were less desirable, as he exited with a 3.33 WHIP, a .412 opponents' batting average and .500 on-base percentage.

Expected to be a significant piece to the bullpen puzzle, De Los Santos was plagued by mechanical issues, as he regularly struggled to find rhythm out of the stretch and didn't record an out in his last three outings. But manager Bob Melvin said he believes his Minor League stint "isn't a long-term thing."

"He's a guy that pitched very well for us last year, has a high ceiling," Melvin said. "It was just to the point now where he was struggling to throw strikes, and when he did, I don't think he had a lot of confidence. We don't have too many guys like him that have the potential to be a late-inning reliever with plus-stuff. We need to get him right, and he understands that."

Only three right-handers currently reside in the A's bullpen, its newest member being Miller, who brings with him a 3.00 ERA and a .188 batting average -- including a .095 mark against right-handers -- with eight strikeouts and two walks in nine innings.

Miller was used in various roles in Sacramento, including closer, but Melvin said he plans to use Miller in a long-relief role. Miller, 29, is just happy for the opportunity.

"I was sitting down in the clubhouse last night when [manager] Darren Bush walked in and told everyone, 'Hey, somebody's going up tomorrow,'" Miller recalled. "He reached out and shook my hand, and I was a deer in headlights. Totally wasn't expecting this at all."

It's safe to assume Thompson wasn't, either. The right-handed Aussie pitched just two-thirds of a scoreless inning for the A's before being designated for assignment on Wednesday, and Melvin simply said the decision was based on "an influx of roster moves.

"It's too bad," Melvin said. "It certainly wasn't a performance-based thing. It was just more a numbers game than anything else at this point. And when you're out of options, you have the designation. Really, I'd like to see him again. We'd like to see him get to Triple-A and have the option to bring him back."

Hughes out with flu-like symptoms

OAKLAND -- Eric Sogard jumped on the third-base merry-go-round on Wednesday, as recent acquisition Luke Hughes sat out with a 102-degree temperature.

A's manager Bob Melvin is hopeful that Thursday's off-day, when the team travels to Baltimore in preparation of a nine-game road trip, will help Hughes recover by Friday.

Despite suffering three errors in his first two games with the A's, Hughes is considered the everyday third baseman for now.

That decision follows the Josh Donaldson experiment, which ended Monday when the infielder was optioned to Triple-A, in the wake of his offensive struggles. The A's, attempting to offset the loss of an injured Scott Sizemore, are hoping Hughes sticks.

"We have who we have, and we're going to take a hard look at Luke Hughes," Melvin said. "We did the same thing with Donaldson, and that doesn't mean he won't be back at some point in time. But [Sizemore's injury] created a bit of a hole for us, and Sizemore was the guy we expected to get 550 at-bats and play the majority of the time.

"Certainly you'd like someone to go in there and do the job and be able to write him in every day. We're just not there right now."