Curtis was optioned to Double-A Arkansas on Saturday.
After two stellar outings for the Mariners earlier in the year, Curtis struggled Friday night, uncorking two wild pitches, hitting a batter and serving up a home run in a three-inning outing. Now that he's likely unavailable to pitch for the next few days, he'll return to the minors in favor of Rob Whalen, a fresh arm recalled from Triple-A Tacoma in a corresponding move.