Parker, who will have a scan on Wednesday, went to the Spurs locker room during the third quarter and re-entered the game briefly in the fourth quarter before returning to the bench with his team comfortably ahead.
"I don't know, I have no idea. We'll do an MRI tomorrow and hopefully it's nothing big and it's just a little cramping or it got tight on me," Parker said.
"It was just a weird feeling and I just went to make sure I was okay and then I played like two minutes in the fourth quarter and we were up big so Pops (coach Gregg Popovich) didn't want to take no risks."
Losing Parker, who leads the team with 22.3 points per game in the post-season, could be a blow for a Spurs team who are two wins away from their first NBA title since 2007.
Parker had six points in the Spurs' win on Tuesday in the third game of the best-of-seven finals.
Game Four is on Thursday in San Antonio.
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