ARLINGTON -- The Mariners' bullpen has logged a lot of innings the past eight days, forcing a roster move on Saturday that cost Chris Shelton his job as a reserve infielder.

He was designated for assignment to make room for left-handed pitcher Luke French, one of the two players acquired from the Tigers on Friday for left-handed starter Jarrod Washburn.

"Because of the lack of quality starts we've had, the bullpen has taken the brunt of the innings and we need to get back to 12 pitchers," manager Don Wakamatsu said. "This gives us that opportunity."

The Mariners had been operating nicely with an 11-man pitching staff going into and coming out of the All-Star break, primarily because right-hander Felix Hernandez and Washburn were pitching into the seventh inning in practically all of their starts.

But beginning with the series opener against the Indians on July 24 at Safeco Field, the starters have averaged 4.9 innings over the past eight games. And with Washburn gone, an even heavier burden could fall on the bullpen.

Left-hander Garrett Olson, who has been in and out of the rotation and started Thursday night's game against the Rangers, will move back to the bullpen and French moves into the starting rotation. He'll make his Mariners debut Wednesday night against the Royals in Kansas City.

Olson was available on a limited basis in Saturday night's game.

Shelton appeared in nine games since being recalled from Triple-A Tacoma on July 9 and was hitting .231 (6-for-26) with four RBIs. He was hitting .319 with 23 doubles, one triple, 12 home runs and 64 RBIs in 76 games with Tacoma this season.

Seattle has 10 days to trade, release or outright Shelton to the Minors.

"With Adrian [Beltre] coming back in a few days [Tuesday], I had an idea it might be me," Shelton said. "I'm not surprised it happened, but a little surprised it happened [Saturday]."

The 29-year-old Shelton, who has previous big league experience with the Tigers and Rangers, said he would return to his Salt Lake City home for a couple of days and "wait to see what happens."

"Obviously, if someone picks me up, I would go to another organization, but if not, I more than likely would go back to Tacoma, finish out the year and see what happens in September."