"We'll know more probably tomorrow," Ausmus said on Friday.
Martinez left Thursday's game for a pinch-runner in the seventh inning, which isn't out of the ordinary for the slow-footed designated hitter, but he complained of cold sweats, dizziness and an accelerated heartbeat.
Ausmus said Martinez first mentioned the symptoms to head athletic trainer Kevin Rand after his second at-bat of the game. The initial thought was that Martinez was simply dehydrated on a warm, humid night, but the symptoms continued after the game, long after Martinez had retreated into the air-conditioned clubhouse and taken in fluids.
Ausmus said he noticed Martinez slouching on his way to first base his final at-bat. He talked with Martinez earlier Friday.
"It's a little bit scary," Ausmus said. "It's not something that, at his age, you generally consider an issue or worry about. That being said, I guess he's making it through. I think there's a little bit of an unknown factor, which is causing more anxiety than anything else."
The 38-year-old Martinez is batting .261 (57-for-218) with 10 doubles, five home runs, 29 RBIs and a .714 OPS.
With Martinez on the DL, the Tigers called up catcher/first baseman John Hicks from Triple-A Toledo. The Mud Hens are at home this week, allowing Hicks to join the team in time for Friday's game.
As for Martinez's DH slot, Ausmus said he plans to use it to give other ailing Tigers some games to get off the field without losing at-bats. Miguel Cabrera tops the list with a sore back, left hip flexor and groin issues, but Alex Avila and J.D. Martinez could also see time there.