OAKLAND -- Rich Harden is finally going to see his first game action since signing a one-year, $1.5 million contract with the A's in the offseason.

Sidelined all season with a strained latissimus dorsi muscle, Harden will make his first rehab start Monday with Triple-A Sacramento, A's manager Bob Melvin said.

Given the A's current situation with their rotation, Harden will be stretched out as a starter, a role he is accustomed to. Aside from Harden, four starters -- Brett Anderson, Dallas Braden, Brandon McCarthy and Tyson Ross -- are on the disabled list for various injuries to their throwing arms.

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While Harden will take the mound Monday in Sacramento, two of the other injured A's starters are working their way back from the disabled list.

Ross, who has been sidelined with a strained right oblique, threw another bullpen session before Friday's game. The righty tossed two simulated innings and, including warmups, threw roughly 70 pitches.

"It's coming along," Ross said. "My arm got out of shape for a minute there, but it's been feeling pretty strong. I got my command back the last two outings in the 'pen. I'm feeling pretty good."

Ross will next throw in four days when he will pitch a simulated game and face hitters for the first time since his injury on May 19. After that, it is unclear what the next step in his recovery will be, saying the team will take it one step at a time as long as his arm is feeling well.

Meanwhile, McCarthy, who has a stress reaction in his right shoulder, will throw against live hitters Saturday. The righty said his shoulder is feeling well so far and that he is scheduled to throw between 60 and 65 pitches from the mound.

Willingham aggravates Achilles tendon strain

OAKLAND -- Left fielder Josh Willingham left Friday night's 5-2 A's win over the Giants in the seventh inning with a strained left Achilles tendon.

Willingham aggravated it while pushing off third base to score in a two-run third inning for the A's. Earlier in the frame, Willingham hit an RBI double and then swiped third base.

The slugger has dealt with the injury before in his career but said it has never felt this bad. The injury flared up in a game against the Red Sox during the team's recent 10-game road trip and Willingham was given a day off in Chicago to rest it.

This time around, Willingham will likely miss multiple games, meaning he'll be out for the remainder of the series against San Francisco, a team he is hitting .309 against for his career.

"I don't know how long, hopefully just a couple games," Willingham said. "It's hard to say. That's what I'm hoping, just rest it a couple days."

With Willingham sidelined, the A's have multiple options to fill the void in left field, including Conor Jackson -- who took over the position in the seventh inning Friday -- and Ryan Sweeney. It is also possible that designated hitter Hideki Matsui could see time at the position, though A's manager Bob Melvin said he would be more likely to use Matsui in right field during Interleague Play.

Ellis to get back to work in rehab outing

OAKLAND -- A's second baseman Mark Ellis, nursing a strained right hamstring, is slated to begin a three-game rehab assignment with Triple-A Sacramento beginning Saturday.

Barring any setbacks, Ellis is fully expected to be activated from the 15-day disabled list when eligible Wednesday, when the A's are scheduled to take on the host Mets at Citi Field for the second of a three-game set.

Where that leaves red-hot rookie Jemile Weeks is unknown at the moment. Neither manager Bob Melvin nor general manager Billy Beane is tipping his hand about the second-base situation. It's a tricky one, considering Ellis' veteran status as the club's longest-tenured player and Weeks' immediate production at the plate, where he entered Friday hitting .344 with three triples and five runs in nine games.

"That will work itself out," Ellis said. "That's all I can say. It's never a problem to have too many good players. That'll all take care of itself."

A possible scenario that doesn't involve the moving of Ellis or the demotion of Weeks is optioning the struggling Daric Barton to Triple-A Sacramento. Barton, who did not start Friday, is hitting just .212 with a Major League-worst .264 slugging percentage. He's also homerless in his first 63 contests as a first baseman, marking the longest such streak since Sean Casey also matched that total at the start of the 2007 campaign.

"Nothing's been going right all season," Barton said. "It's a grind, and it's one of those things you have to go through and just figure out a way to get out of."

Still, a Barton transaction wouldn't guarantee everyday playing time for both Ellis and Weeks at second base, something the organization would likely prefer to see.

Henderson teaching A's about baserunning

OAKLAND -- Rickey Henderson spent 25 seasons tormenting opposing teams on the basepaths, 14 of them with the A's. Now the Hall of Famer is mentoring some current A's players in the art of swiping bags.

At the behest of A's manager Bob Melvin, Henderson, the all-time Major League leader in stolen bases (1,406), spent time Friday with his former ballclub in the clubhouse and on the field during batting practice before the resumption of the Bay Bridge Series.

"There's a wealth of information that he has," Melvin said. "That's something I'd like to see more of, to get the former A's and the championship A's here. There's something to be said about having winners around your guys."

Henderson was a member of two World Series champions, the 1989 A's and the 1993 Blue Jays, and Melvin hopes Henderson passes on his wisdom to players like Coco Crisp, Cliff Pennington, David DeJesus and rookie Jemile Weeks.

"He stole a lot of bases -- that's the end result of it -- but he did more than that because he took the focus off the hitter," Melvin said. "A lot of times your focus is on the runner, you hang a pitch and it's a two-run homer.

"More than just the basestealing part of it, he took, completely like no other, took your mind off the pitcher-catcher relationship and trying to get the hitter out because you were so worried about him at first base or second base."

Baserunners like Henderson come few and far in between, but the Hall of Famer believes the A's have the talent to be a good stealing team with the quartet of speedsters on the roster. Entering Friday, Crisp was fourth in the Majors with 20 stolen bases while Weeks swiped his first one Wednesday.

"Them guys can run," Henderson said. "The kids aren't running as much now because they're so afraid to get thrown out. They need to get away from being afraid of getting thrown out."

Although fearlessness is something that can't be taught, Henderson also wants to teach the players something tangible to help them become more successful. Specifically, he wants to work with them on getting a good jump when attempting to steal.

"The kids now concentrate on hitting, concentrate on trying to do our fielding and we forget about what baserunning means to the ballclub and what it means to you as an individual," he said. "I think they need to pay a little more attention to working on getting a good jump."

Matsui downplays approach to 500 homers

OAKLAND -- Hideki Matsui's surging presence at the plate has culminated in three home runs during a seven-game stretch, putting him on the verge of career home run No. 500 between the U.S. and Japan.

Entering Friday's series opener against the visiting Giants, Matsui stood just one homer shy of reaching the rare plateau, one he insists he's not overly concerned about.

"Really, I'm not thinking about it," Matsui said through translator Roger Kahlon. "In my mind, even if it's No. 500, the majority of them were hit in Japan, so I separate the two. Honestly speaking, it's really something that's not in my mind."

Of Matsui's 499 career long balls, 167 have come on the Major League stage during a nine-year playing career. A total of 25 big leaguers have hit 500 home runs and eight players have done it in the Japanese Leagues, but Matsui would be the first one to combine the two.

The 36-year-old veteran has tallied six homers as a member of the A's, and he's also 7-for-23 with five walks and seven RBIs over his previous seven contests following a disappointing 4-for-40 stretch. Much of that success potentially stems from newly named manager Bob Melvin's decision to make him the club's everyday designated hitter, no matter the opposing hurler.

"Over the past week, I've been feeling pretty good at the plate," Matsui said. "I think being able to get consistent at-bats and play every day, that has helped mentally."

One of Matsui's biggest fans showed up at the Oakland Coliseum on Friday and marveled at his looming 500th home run.

"That's a great feat," A's great Rickey Henderson said. "Achieving that goal, that's just the ultimate."