Brandon McCarthy's troublesome right shoulder is acting up again.

McCarthy, a Glendale native and starting pitcher for the Oakland Athletics, was placed on the disabled list Sunday with a sore shoulder. The move was retroactive to Friday.

McCarthy missed nearly seven weeks last season with a similar injury and has spent several stints on the disabled list throughout his career because of his ailing arm.

''This is just a lot of soreness and fatigue. For some reason, it's what I run into this time of year almost every year,'' McCarthy told the Associated Press prior to Sunday's road game against the host San Francisco Giants. ''I've got to figure out a way to get past this.

"The hope is we're catching it at a point where we can contain it. A couple weeks ago it was really just precautionary. This isn't the same issue. This is just a lot of soreness and fatigue."

The Athletics conducted an MRI last week on McCarthy's shoulder, which revealed no structural damage. McCarthy had a stress reaction in his scapula last year, which sidelined him nearly two months. Fortunately for the Athletics, McCarthy escaped the injury bug the remainder of the season.

McCarthy, who is eligible to come off the disabled list June 2, is 3-3 with a 2.95 earned-run average in nine starts. He's struck out 40 and walked 16 in 58 innings.

The timing of McCarthy's latest ailment comes at a time when he's pitched well for Oakland, which entered Monday night's home game against the Los Angeles Angels of Anaheim at 21-21 and in second place in the American League's West Division behind the Texas Rangers.

He's gone at least five innings in each start. McCarthy last pitched Thursday against Texas, giving up four runs and eight hits in 5 1/3 innings. McCarthy, who allowed two home runs, didn't figure in the decision.

McCarthy, who previously pitched for the Chicago White Sox and Texas, had won his three previous starts. He beat the Baltimore Orioles on April 27, followed by victories against the Boston Red Sox on May 2 and Detroit Tigers on May 12.

''I think there's a certain feeling that he has when the stress reaction comes on,'' A's Manager Bob Melvin told the Associated Press. ''At least from what he's been saying to us so far, it's not bad.''

McCarthy is 32-36 with a 4.06 ERA in his career. He's struck out 414 in 601 1/3 innings.

charles.rich@latimes.com