Some discomfort behind his left knee has delayed left-hander Jarrod Washburn’s next start.

He was supposed to face the Giants in an Interleague Play game on Saturday night at Safeco Field, but has been pushed back to Tuesday night’s game against the Athletics in Oakland.

Left-hander Garrett Olson will pinch-hit for Washburn against the Giants.

Washburn, who is 3-3 with a 3.86 ERA, worked five innings against the Angels last Monday night, surrendering six earned runs – five of them in the fifth inning.

“He’s had some tightness in his back knee pushing off a little bit,” manager Don Wakamatsu said prior to Friday night’s series opener.  “The last outing, I saw a little bit where it seemed like on the change-up he couldn’t ride it through.

“Everything checked out fine. I think it’s just at this point it’s a little safer to back him up a couple days. It’s been feeling better, but at this point we’d like to eliminate it and just take a couple extra days.”

This will be Olson’s second start of the season. He went six innings against the Red Sox on May 16, surrendering four hits and five runs in a 5-3 Mariners loss at Safeco Field.

— Jim Street