Parker, San Antonio's lone All-Star this season, exited with 8:45 remaining in the second quarter and the Spurs up six points.
The Spurs rolled to a 104-82 rout without Parker, who wasn't available for comment after the game.
San Antonio coach Gregg Popovich said he didn't have any details on the severity of Parker's hamstring problem, but several Spurs said they were optimistic that their point guard would be ready for the Western Conference finals against the Oklahoma City Thunder or Los Angeles Clippers.
"Luckily, we have a couple of days," power forward Tim Duncan said. "It worries us obviously, but he's been going hard, had a great series thus far and it just kind of caught up to him. They pulled the plug on him before he hurt himself. He started to feel a little weird and I think they did the right thing, pulled the plug on him, so hopefully that helps him. Hopefully, there's nothing there."
Parker, who was scoreless in 10 minutes during the first half, entered Wednesday night averaging a team-high 21.0 points and 5.4 assists this postseason. He averaged 23 points and 6.5 assists as San Antonio took a 3-1 series lead over Portland.
The Spurs went 11-3 in games Parker missed during the regular season, a winning percentage of .786. San Antonio was 51-17 (.750) when Parker played.