Maurer was originally slated for that spot, but he will work instead as the long man in the bullpen in the Rangers series and then rejoin the rotation when Seattle returns home for an 11-game stand at Safeco Field.
The Mariners will face the Astros in a four-game set to start that homestand, with Roenis Elias slated for Thursday, Felix Hernandez on Friday, Maurer on Saturday and Iwakuma on Sunday.
Maurer is 1-2 with a 6.00 ERA in five starts, and he lasted just 3 2/3 innings against the Rays in his latest outing.
"Right now we have guys that are throwing a little better," manager Lloyd McClendon said. "This gives him a chance to get rested up, it gives us some help in the bullpen and he'll be back in there on the next turn."
The Mariners are intrigued by Maurer's potential but are still waiting for results at the big league level.
"Obviously the next step is up to him," McClendon said. "You've got to go out and get it done. We can talk about how close he is and the intangibles he brings and the stuff. Ultimately he has to perform on the field. But yeah, I think he's close."
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.