Doncic dealt with the injury in Dallas' 126-118 defeat to the Miami Heat on Friday.
"I didn't know how important the thumb was to hold the ball," he told reporters after the game. "It was tough. ... I wasn't myself today. Just have to learn from that and move on."
The 20-year-old is averaging 28.6 points, 9.4 rebounds and 8.8 assists through 48 games.
In his second NBA season, Doncic has dealt with nagging ankle injuries that have cost him 12 games. He most recently missed seven straight games to close January and open February to give the ankle additional rest.
"That's just the nature of the injury. There's being injured and there's being hurt. He's not injured, but it's going to hurt," Mavericks owner Mark Cuban told reporters.
The likes of Tim Hardaway Jr. and Seth Curry will have to pick up additional slack with Doncic out of the lineup.