Nowitzki suffered the injury when he was called for a foul after stripping Miami's Chris Bosh with 3:44 remaining in the fourth quarter.
"I thought I stripped him clean, then I kind of looked down and I couldn't straighten my finger out anymore," said Nowitzki, who had 27 points on 7-of-18 shooting as the Mavs fell behind in a series for the first time this postseason. "So I tore a tendon in there. I guess it will be all right. I have to wear a splint probably the rest of the playoffs."
Nowitzki, who is averaging 28.3 points per game in the playoffs, said X-rays on the finger were negative.
He downplayed concern about the injury, pointing out that it's on his non-shooting hand.
"I'll be all right for Thursday," Nowitzki said, referring to Game 2.
Overall, the Mavericks made 37.3 percent of their shots, worst of the postseason. So they're going to need Nowitzki to be as accurate as possible in Game 2 to keep the series from slipping away.
When informed of the injury, Miami's LeBron James shot down the notion it could negatively impact Nowitzki's offensive game.
"That left hand is just a guide hand for all shooters," James said. "We all know that. It won't affect him. He's still going to be great. He's still going to be Dirk."
Tim MacMahon covers the Mavs for ESPNDallas.com.