The Rays' closer retired two of the first three hitters he faced before giving way to Dan Wheeler, who got the final out in Tampa Bay's 5-3 win over Texas.
"We sent him out to get an MRI, so we'll know more tomorrow," Rays manager Joe Maddon said.
Percival has played an integral role in the Rays' success both on the field, where he has 14 saves, and in the clubhouse, where he has added a veteran presence.
"Obviously we're all concerned [about Percival]," Carlos Pena said. "Everybody in here has been to the training room to see how he's doing."
Wheeler was among those who saw Percival after the game.
"He seemed in good spirits," Wheeler said. "He didn't seem to think it was too bad, so hopefully we can hold the fort down while he's gone and we can continue this winning baseball. ... We need him, and hopefully, it's just a couple of days. I don't know what the MRI will show. We're just keeping our fingers crossed."
Wheeler or Al Reyes will likely fill the closer role in Percival's absence.
"Whatever role they need me to do, I'll do," Wheeler said. "That's the way I've done it always. I have a little experience. Reyes has a little experience. So I think we've got some quality arms who can go out there and get the job done."
Bill Chastain is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.