SAN FRANCISCO -- Milton Bradley, who hasn't played on a regular basis for the A's since late April, was placed on the 15-day disabled list Friday, with a strained right calf, before the opener of a three-game Interleague series against the host Giants at AT&T Park.

Bradley was on the DL from April 23-May 10 with a strained left hamstring, and after returning for a weekend series in Texas, he landed back on the DL from May 15-29 after having aggravated the injury.

Last Saturday, however, Bradley had to leave in the fifth inning of a game against Minnesota after hurting his calf. He was given a few days off to heal up, and he was in the starting lineup that was posted before Wednesday's game against the Red Sox, but the calf tightened up during batting practice and he was a late scratch.

"I feel bad for him," A's manager Bob Geren said of Bradley, who is batting .306 with two homers and seven RBIs in 18 games. "He's been working real hard to come back."

In addition to being Bradley's third trip to the DL this season, it's his fifth trip since joining the A's before the 2006 season, and he's been on the DL 11 times since breaking into the big leagues with the Montreal Expos in 2000.

To fill Bradley's spot on the 25-man roster, the A's again recalled infielder Donnie Murphy, who was recalled for the first time this year when Bradley went on the DL for the second time. He was optioned back to Triple-A Sacramento when outfielder Mark Kotsay was activated off the 60-day DL on June 1.

In 30 games with Triple-A Sacramento this season, Murphy was batting .342 with two homers and 15 RBIs.

Battling buddies: A's righty Dan Haren and Giants lefty Barry Zito, fast friends during their two seasons together in Oakland, will square off for the first time Saturday.

"We just missed each other the last time around," Haren said, referring to the A's-Giants series in Oakland three weeks ago. "It'll be a little extra special because I respect him so much. I really think highly of him."

Not high enough to groove him a series of batting-practice fastballs, however. Zito hired former Orioles leadoff man Brady Anderson as his personal hitting coach over the winter, and Haren has seen a dramatic improvement in the swing that produced one hit in 29 at-bats over seven seasons in the American League.

Zito is batting .125 (3-for-24) this season.

"He looks 10 times better," said Haren, who is 4-for-49 (.082) with three doubles in his career. "He looks like somewhat of an athlete now. ... So I can't just lay it in there for him. I'm definitely going to throw him a splitter or two, and I hope he throws me at least one curveball."

"He better not throw me all fastballs," Zito said with a smile. "I can rake now. And he's definitely going to see a bender, 'cause he can hit, too."

Since being knocked around by the A's for seven runs in four innings May 18, Zito is 3-0 with a 0.45 ERA in three starts.

Dribblers: Giants slugger Barry Bonds has been slumping a bit of late, but Geren said the A's won't change their general approach to pitching against him. "It depends on the situation," he said. "He's still a threat to hit a home run every time he steps into the box." ... Disabled righties Huston Street (elbow) and Rich Harden (shoulder) had good workouts Friday. Harden is expected to come off the DL within a couple of weeks and build up his pitch count while working out of Oakland's bullpen, and Street is optimistic that he'll be back by the All-Star break (July 9-11), if not sooner. ... Designated hitter Mike Piazza (shoulder), who has been hitting off a tee, will go on a Minor League rehab assignment before being activated from the DL. Geren said he expects Piazza back by the All-Star break, too. ... Jack Cust, who set the world on fire for two weeks as Piazza's fill-in at DH, was batting .156 (7-for-45) over his previous 15 games going into the series, but Geren said Cust might get a start in the outfield here.

Up next: Haren (6-2, 1.70 ERA) and Zito (6-5, 3.87 ERA) meet Saturday in the second game of the series. The first pitch is set for 12:55 p.m. PT.