Manager Bob Melvin said "his results are starting to get pretty impressive."

Nakajima is batting .383 with two homers and five RBI in his last 10 games with Triple-A Sacramento. He was activated off the disabled list in late May and optioned to Sacramento. 

Manager Bob Melvin wants Nakajima to play as many positions as possible in order to make him more versatile at the major-league level in the future. His 20-day rehab assignment is up Wednesday and the A's will make a decision on him at that time. Nakajima is batting .250 at Triple-A with five RBI over 40 at-bats. 

"He's going down the line 100 percent and moving good on defense," Melvin said. "Next up for him is to get multiple-hit games back-to-back."

Nakajima's rehab assignment can only last until May 23, at which point he'll either have to be placed on the active roster or assigned to the minor leagues. He's recovering from a left hamstring injury.

Nakajima will take Wednesday off and then play four games in a row. He's gone 7 for 29 (.241) overall with the River Cats. 

"From everything that I hear, he's getting more and more comfortable, not only in the field but at the plate," manager Bob Melvin said. "We want to make sure he gets plenty of at-bats and plays plenty of games to where he doesn't have to feel the hamstring."