KANSAS CITY, Mo. -- The A's cleared a roster spot for outfielder Yoenis Cespedes on Thursday by optioning pitcher Tyson Ross to Triple-A Sacramento.
Cespedes is expected to be activated from the disabled list for Friday's series opener at Kansas City.
Ross was sent down a day after another shaky start by the right-hander.
Ross was 2-6 with a 5.94 ERA in nine starts this season. He gave up four runs and three walks in five innings Wednesday in a loss to Minnesota, and he had a 7.34 ERA over his past seven outings.
Ross, who went to Bishop O'Dowd High in Oakland, has been one of the A's top pitching prospects since being drafted in the second round in 2008 out of Cal. But command problems have kept him from cementing his status in the rotation.
He is 6-13 with a 4.86 ERA in 44 career big league appearances (17 starts) and has averaged four walks per nine innings.
Oakland will need to clear another spot Saturday, when right-hander Brandon McCarthy is slated to come off the D.L. and start against the Royals.
One option to fill Ross' spot in the rotation is left-hander Travis Blackley, who allowed one run over five innings in a spot start Monday at Minnesota.
Ramirez is hitting .222 (8-for-36) with no extra-base hits