It's uncertain how severe the sprain is or how much time Haywood could miss.
After the game, Haywood said he suffered a "simple sprain" to his left ankle. He said there is a little swelling and that he'll wait to see how it responds Tuesday morning before determining if he can play against Tyson Chandler and the New York Knicks back in Dallas on Tuesday.
The 7-footer drove by Thunder center Kendrick Perkins and got a shot off at the rim, but Haywood missed it and came down in pain. He had to hobble all the way down the floor and intentionally foul Thunder forward Kevin Durant just to get the game stopped.
"He rode me the whole way to the basket," Haywood said of Perkins.
Haywood then hopped back down the floor and headed to the locker room with head athletic trainer Casey Smith.
Ian Mahinmi stepped up big in relief, scoring 13 points -- all in the first half -- and added five rebounds, two assists and two steals.
Jeff Caplan covers the Dallas Mavericks for ESPNDallas.com.