Russell Branyan, who has fought persistent back pain much of his career and all of this season, was pulled from the lineup Friday - and placed on the 15-day disabled list tonight.
Branyan has a herniated disc in his back and the team hopes their leading home run hitter can return by mid-September.
That means just as Ichiro and Adrian Beltre return for a run through the American League West - a trip that takes Seattle through Oakland, Los Angeles and Texas - Branyan will miss all of it.
For now, Jack Hannahan, a third baseman by trade, will play first base.
With Branyan going on the DL, the team recalled reliever Chris Jakubauskas from Tacoma.
On Tuesday, when rosters expand, the Mariners will bring up a handful of minor league players - from Brandon Morrow to Garrett Olson.They will also bring up a first baseman, probably rookie Mike Carp.
With their season still in the balance - 33 games left, including tonight, with a 67-62 record - losing Branyan is a body blow.
Without him, the Mariners have only one player with as many as 55 RBI, Jose Lopez. Without him, their leading home run hitter is Lopez, who has 19 homers.They've played without most everyone on the roster at one point or another - Felix Hernandez being the exception - and they will play now without Branyan.
It makes a tough September schedule all the more difficult.