Hernandez allowed four runs and six hits in Seattle's 19-9 loss to the Tigers. There was no injury announcement after he was removed from the game, but afterward, Mariners manager Scott Servais said the right-hander was dealing with stiffness.
"He had some stiffness in his shoulder going out for the second inning, but there wasn't any pain," Servais said. "He said it was more like a dead arm, but there's obviously some concern when you are talking about a pitcher's shoulder. He's been a horse for us, but we have to get this checked out."
Hernandez made at least 30 starts for the Mariners every season from 2006 through 2015. He made 25 starts last season, when he missed nearly two months with a calf injury.
"We should know a lot more in a couple days," Servais said. "At this point, it's just a dead arm."
Seattle is on the second stop of a 10-game trip. The Mariners have five more games to play against the Tigers and Cleveland Indians before returning home.