Nowitzki attempted to run at practice on Thursday, but he experienced pain and was told by the team's medical staff to shut down the workout.
When Nowitzki sustained the injury on Dec. 27 in a game at Oklahoma City, he thought he'd be out for only a short time. But he hasn't healed as quickly as he hoped, and remains listed as day-to-day.
"I guess I don't have a lot of experience with knee injuries -- and that's a good thing," Nowitzki told the Dallas Morning News. "I never thought when this first happened that I was going to miss two weeks ... I guess I took the situation a little too lightly."
Nowitzki averages 24.1 points.
Earlier in the week, the Mavericks learned that No. 3 scorer Caron Butler was probably out for the season with a torn tendon in his right knee.