Gordon was placed on the IL on Tuesday, a day after leaving following the second inning of a win over Texas. Gordon said he strained the muscle rounding first base.
It's the second time he's been on the injured list this season after a 19-game stint in May and June with a bruised right wrist.
"This is crazy," Gordon said. "I've got some bad luck or something. I need to do something different in life."
Gordon is batting .280 with 16 stolen bases.
"It's going to be a few weeks," Seattle manager Scott Servais said after Gordon had an MRI. "I don't have an exact timeline."
With second base prospect Shed Long injured, the Mariners selected the contract of infielder Tim Lopes from Triple-A Tacoma and designated right-hander reliever Parker Markel for assignment.
Lopes would be the 12th Mariners player to make his major league debut this season.