Williams aggravated an abdominal strain and sports hernia during the first minute of the game and checked out for good at the 10:31 mark of the first quarter.
"I think he's done for the year," coach Rick Carlisle said after the Mavericks' loss to the Thunder. "That's what I think. I don't expect him to play in Game 5."
Williams missed Game 3 because of the abdominal strain and sports hernia, which could require offseason surgery.
His hot start in Game 2, when he scored 11 points in the first five minutes, was critical to the Mavs' lone win of the series. However, he exited that game midway through the third quarter, clearly in excruciating pain.
Williams missed eight games late in the season because of the ailment. He returned after J.J. Barea suffered a strained groin, and his 23-point, six-assist performance against the Utah Jazz helped the Mavs clinch a playoff berth.
Williams, who averaged 14.1 points and a team-high 5.8 assists per game this season, can opt out of the second year of his contract this summer.