Rasmus, who has 67 hits, 11 home runs and 42 RBIs this season, has been out of the Astros' lineup since Thursday with an ear infection.
"He hasn't been able to do much of anything," Astros manager A.J. Hinch said. "... It's unfortunate. Some of the matchups [have been] pretty good for him.
"He doesn't look like he feels well," Hinch said. "We've all been around people with inner ear infections or [who are] under the weather or whatever. He definitely doesn't look right, but I told him I just need him to be right for maybe one pinch-hit [Sunday]."
Feldman left Saturday afternoon's game in the top of the ninth with back stiffness. The veteran pitcher has emerged as a quality relief pitcher for the team after starting the season as a member of the rotation and struggling.
"Nothing is going to change [with Feldman] for a while," Hinch said. "He's unavailable today because [he pitched yesterday]. We'll have a little bit more of an understanding of what's going on with him by the time we get to Seattle."
Entering Saturday's game in the fifth inning, down 3-0 to the A's, the right-hander allowed only two hits over 3 2/3 scoreless innings. Hinch said after the game that pulling Feldman in the top of the ninth was mainly precautionary and that he is day to day.
"I think the All-Star break comes at the right time all the time," Hinch said. "It's such a grind for these guys and for us to play the first half of the season. It's a sprint race, and then these four days are really important for us. ... We need it physically [and] mentally to rejuvenate ourselves for a really fun back half of the season."
Jordan Ray is a reporter for MLB.com based in Houston. This story was not subject to the approval of Major League Baseball or its clubs.