Mason was ruled out for 2-to-3 weeks Tuesday after undergoing arthroscopic surgery on his right knee, Sam Carchidi of the Philadelphia Inquirer reports. He's been placed on injured reserve.Mason has been incredibly banged up this season, having previously missed a total of 10 games due to separate lower-body injuries. Despite his less-than-optimal health, he's been one of the top performers on an underachieving Flyers squad, producing a 2.30 GAA and .925 save percentage over 34 games. Backup Ray Emery will slide into the No. 1 spot on the depth chart for at least Tuesday's game against the Canadiens, but AHL Lehigh Valley goalie Rob Zepp could also see additional duty once he recovers from a right leg injury.