Nowitzki said earlier in the week that he hoped to avoid surgery after injuring the knee early in training camp. He has played in only one of the team's four exhibition games.
An absence of six weeks would mean Nowitzki would return in early December and miss about 16 games during the regular season.
Dallas opens its campaign Oct. 30 at the Los Angeles Lakers.
Nowitzki is in his 14th season with the Mavericks and has averaged at least 20 points a game every year since the 2000-01 campaign. He has scored 24,134 points during regular-season games, another 3,321 points in playoff action and has been a member of the All-Star team 11 times.
He was named MVP of the 2011 Championship Series when the Mavericks defeated Miami to win the franchise's only NBA title.