"I felt it when I went to third on that play," Cruz said. "So I stretched it out and tried to do a skip, and it felt OK, and then like the third step when I tried to get to home plate, that's when I felt it [again]."
Cruz said he would have scored on the play if he'd been able to go full speed.
"Of course," he said. "That's like an extra two steps."
Cruz, who leads the Majors with 39 home runs and tops the Mariners with a .310 batting average and 82 RBIs, said he'll use Thursday's off-day to ice the leg and then be reevaluated on Friday.
Manager Lloyd McClendon said he didn't believe the injury was too serious, but that the team would know more after Cruz is checked out again in Oakland.
Cruz struck out his first three at-bats on Wednesday before singling in the seventh and then moving to third when Seager got caught in the rundown.
Cruz then tried to score on Trumbo's flyout to right field, but was tagged out by catcher Hank Conger for the third out of the inning.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB, read his Mariners Musings blog, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.