The 7-foot-3 forward departed Thursday's victory over the Brooklyn Nets in the third quarter. He underwent an MRI exam on Friday and was diagnosed with a twisted knee.
Porzingis said after the contest that he initially injured the knee in the first half. He later departed when the knee didn't feel stable.
"I felt my knee buckle a little bit, and I felt a little pain there, so it's more about being cautious," Porzingis told reporters. "I had a little shock pain there, and that's it."
If Porzingis is sidelined against the Thunder, he will miss the return of former Knicks star Carmelo Anthony to Madison Square Garden. Anthony was traded to Oklahoma City in September.
Porzingis averages 25.5 points, 6.6 rebounds and 2.1 blocked shots.
Veteran Michael Beasley will likely be the starter if Porzingis is ruled out.