ST. PETERSBURG -- For the second consecutive game, Mark Ellis was absent from the A's starting lineup on Wednesday afternoon. The second baseman's right shoulder soreness is expected to keep him sidelined until Friday.

While Ellis has been hampered by shoulder problems in the past -- he missed the entire 2004 campaign with a torn right labrum -- A's manager Bob Geren said he wasn't exercising any extra caution.

"[I'm] really going on how he feels," Geren said. "He knows his body, he knows his arm. He will definitely be ready for Friday."

Ellis said that the problem was nothing major, and told Geren after throwing on Wednesday morning that his arm felt a lot better. The second baseman expected to be fine for Friday's game, which marks the start of a six-game homestand.

A late scratch from Tuesday night's contest against Tampa Bay, Ellis said his arm never "loosened up" after taking grounders prior to the game, and headed off the field to consult with head athletic trainer Steve Sayles.

Ellis also noted on Tuesday that he banged his shoulder on Rays' shortstop Ben Zobrist's shin while sliding into second base on Monday, and the impact -- coupled with his previous history -- is the root of his current arm soreness.

With Oakland's off-day on Thursday, Ellis will be able to recharge his right arm and the club isn't expected to conduct any further treatments.

When the 31-year-old Arizona resident hurt his arm in 2004, Ellis opted for surgery over rehab and was one of baseball's best comeback stories.

"I've known him a long time," Geren said. "I know whether to trust him or not."

Despite recent struggles at the plate -- 6-for-55 over his last 15 games -- Geren believed his second baseman was turning a corner, and penciled Ellis in the leadoff spot on Tuesday, before the scratch.

A cornerstone in the A's middle infield, Ellis has a 50-game errorless streak and currently leads all American League second baseman with a .996 fielding percentage.

The speedy infielder has a career-high 12 stolen bases coming into Wednesday's game, and was tied with Rajai Davis (who previously had four steals with the Giants) for the team lead.