"Where our bullpen has been, the overuse of those guys, we thought we needed a fresher arm," manager Scott Servais said. "Tony's been throwing the ball really well, so we'll get him in there."
Zych pitched a scoreless seventh inning in Tuesday's 5-1 loss to the Yankees, allowing two hits and striking out one.
Zych had been out since May 2 with rotator cuff tendinitis. He pitched in four rehab games, most recently making two hitless one-inning appearances for Tacoma.
The Mariners had been down a pitcher since they placed right-handed reliever Drew Storen on the 15-day DL Monday, retroactive to Saturday, and recalled rookie outfielder Guillermo Heredia from Triple-A.
Romero replaced first baseman Dae-Ho Lee on the active roster on Friday, when Seattle optioned Lee to Triple-A to work on his swing. Since being recalled, Romero had started one game at first, and he went 1-for-2 with a walk and an RBI.
"I didn't necessarily see this coming when we brought him here," Servais said.
Without a right-handed first baseman to platoon with Adam Lind, the Mariners will have to get creative against left-handed pitching. Lind started Tuesday with CC Sabathia on the mound. Lind entered hitting .467 with four RBIs in 15 career at-bats against the left-hander.
Against lefties that Lind has less of a promising history with, Servais said utility Shawn O'Malley could see time at first.
Maddie Lee is a reporter for MLB.com based in Seattle. This story was not subject to the approval of Major League Baseball or its clubs.