X-rays taken during Monday night's game were negative. Afterward, Nowitzki said for the first time that the knee had been bothering him for about two weeks.
"So maybe that's why it gave in a little bit," Nowitzki said. "Hopefully it's just a strain, and hopefully I'll be back in action soon."
His status for Tuesday night's home game against Toronto is uncertain with a home game against Southwest Division leader San Antonio looming Thursday.
Nowitzki left Monday's game at the 9:10 mark of the second quarter after his momentum from a fallaway jumper caused him to stumble backward to the floor. He was fouled on the arm by Thunder center Serge Ibaka, but it appeared that Nowitzki tripped over his own foot, causing him to fall. Despite taking a while to get up and walking gingerly, Nowitzki made the free throw for a 42-36 Mavs lead and then headed to the locker room.
"It was just a scary play," Nowitzki said. "The foul was on my arm so it was just on the landing. I landed awkward and strained it more than I guess it already was. It [the knee] kind of gave in. I don't know what really happened, I've got to look at the play. But, for some reason my knee gave in."
Nowitzki, who is averaging 24.5 points and 7.6 rebounds, had 13 points on 4-of-6 shooting when he exited the game. After he left, the Mavs scored just 14 points and were outscored by the Thunder 20-14 to go into halftime tied 56-56.
After trailing 81-79 after three quarters, the Mavs held the Thunder to 12 points in the fourth quarter to seal their fifth consecutive victory and improve to 24-5.
The 7-foot Nowitzki has been dogged by ankle sprains throughout his career, but none have kept him sidelined long. Nowitzki has remained mostly free of knee injuries with the exception of a left knee sprain that forced him out of the 2003 Western Conference finals for the final three games that the Spurs eventually won in six.
"I'll take an ankle sprain over this any day just because this is a weird injury," Nowitzki said. "I never had it, so from a rolled ankle I probably would have walked it off and came right back out there. We'll look at it and see what it is tomorrow and [take it] kind of day-to-day from this point."