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Dallas Mavericks star forward Dirk Nowitzki will be out at least the next six weeks after undergoing arthroscopic surgery on his ailing right knee Friday.

The Mavericks announced that Nowitzki, 34, is expected to resume on-court activities within approximately six weeks, which means he will miss the beginning of the regular season, about the first 13 games.

Nowitzki missed the past three preseason games with fluid buildup in the knee.

''It's never going to be easy to lose a game-changer for six weeks,'' Mavericks coach Rick Carlisle said. ''We're going to have to make up for it in other areas.''

The knee started to bother the 11-time All-Star during last season’s training camp, but after taking four days off to focus on his conditioning during the lock-out shortened season, it wasn’t an issue the rest of the year.

Nowitzki however had his worst season statistically since his second year in the NBA, averaging 21.6 points and 6.8 rebounds.

The Mavs open the season on the road Oct. 30 against the Los Angeles Lakers, and six of their next eight opponents were lottery teams last season.