Seager, 26, has been one of the Mariners' top players the past two years. He hit .260 with 22 home runs and 69 RBIs in 2013 after batting .259 with 20 home runs and 86 RBIs in 2012.
With Seager out, the Mariners have primarily used Willie Bloomquist, Carlos Triunfel and Nate Tenbrink at third base.
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.