PHOENIX -- Daric Barton, the rookie who's projected as the A's starting first baseman this season, has missed the last four games with soreness on the side of his left hand.

Barton, 22, said that it was diagnosed as a repetition injury from taking too many swings with the bat so early in Spring Training.

Though he took ground balls with the other first basemen prior to Oakland's game Wednesday against the Padres at Phoenix Municipal Stadium, he was again not in the starting lineup.

"I just talked to him about that," said A's manager Bob Geren, who pulled Barton aside as the rest of the team went through its morning paces. "He kind of wants to get back in there, but we want to make sure it's completely healed before he goes back out there."

That could be as early as Thursday, when the A's play the Cubs at home, Geren added, but more likely later in the week.

The A's are counting heavily on Barton to blossom this season as part of their youth movement. He's virtually displaced Dan Johnson, who played 97 games at first base last year. Johnson finds himself this spring trying fend off a challenge for his roster spot from veteran Mike Sweeney, who was invited to camp on a Minor League contract.

The A's are out of options on Johnson to send him back to the Minors, which means he must be traded or released if the A's determine they want to keep Sweeney. Opening up Johnson's spot on the 40-man roster is one way of getting Sweeney on the team. And the A's could keep Johnson if he were to clear waivers, though that isn't likely.

Barton played the 2007 season at Triple-A Sacramento, but was a Sept. 1 callup and started 18 games at first base for the A's, impressing many by batting .347 with nine doubles, four homers and eight RBIs.

He said the root of the injury was a swipe tag at first base last summer when he was still playing for the River Cats.

"I hurt it last year in a collision at first base and missed a couple of days," Barton said. "Then I hurt it swinging again last week. Hopefully, I'll be back in there again in couple of days. I'm going to rest it a couple of more days and then I'll see what I can do."

Spring Training
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It's been a rough week for three-fourths of the projected starting A's infield. First third baseman Eric Chavez had an epidural to relieve inflammation in his surgically repaired back and has been out of action since Friday. Chavez wasn't in camp on Wednesday because his wife was scheduled to have an induced birth for the couple's second child.

Barton apparently hurt his hand on Saturday as the A's romped over the Giants, 23-5, in Scottsdale and hasn't played since.

Finally, on Monday, shortstop Bobby Crosby was scratched from the lineup against the Angels in Tempe because of the back spasms he suffered while taking grounders during batting practice. He's missed two games.

The A's are coming off a season during which the disabled list was utilized 22 times costing players 1,259 games. In addition, with Opening Day against the Red Sox in the Tokyo Dome less than three weeks away, any injury at this point has to be considered a setback.

But Geren said he isn't concerned.

"Camp has been great," he said. "I can't picture it any better than it's been going."