McClendon wouldn't say if two relievers would be added to take their spots, though the club will need to shore up a bullpen that now consists of closer Fernando Rodney and fellow right-handers Danny Farquhar, Dominic Leone and Carson Smith and lefty Charlie Furbush.
Veteran lefty Joe Beimel has been pitching well for Tacoma since joining the club after an extended Spring Training. Beimel has allowed just one hit with no walks and five strikeouts in 3 2/3 scoreless innings in three appearances. He was an integral part of last year's Seattle bullpen, but didn't re-sign until late in the spring after being released by the Rangers.
Veteran right-hander Mark Lowe is another possibility as he's posted a 1.00 ERA in seven games for Tacoma, allowing one run and seven hits over nine innings with no walks and 11 strikeouts. Neither Beimel or Lowe are on the 40-man roster, so moves would need to be made to open spots for them on the Major League club.
McClendon said the moves were made to allow Medina and Olson to get some things squared away in Triple-A.
"In the case of both of them, location and execution is important," he said. "Medina was elevating quite a bit and we need to get some things straightened out. And it's hard to get them straightened out here in the big leagues. That's just almost impossible. Both of those kids need to go down and get a couple things straightened out and they'll be fine."
Medina, 26, is in his third season with the Mariners. He's 1-0 with a 3.00 ERA with four earned runs and 11 hits in 12 innings over 12 appearances this season. Olson, a 25-year-old rookie who made the jump from Double-A, has gone 1-1 with a 5.40 ERA with eight runs and 18 hits in 13 1/3 innings.