Mandzukic was crucial to Bayern's treble last season, scoring 22 goals in 40 matches, and while the Croatian striker has hit the back of the net 12 times in 24 fixtures this term, his future has been shrouded in doubt since confirmation Lewandowski will move to Bavaria from Borussia Dortmund in the 2014-15 campaign.
Speculation is rife in Germany and Italy that Mandzukic will be sold to Juventus during the current transfer window, which will only increase following Beckenbauer's comments on Friday.
"We have many players with which to rotate the squad," Beckenbauer told 11freunde.dr.
"Can Mandzukic be sold after Robert Lewandowski signed for Bayern? In truth, yes.
"Lewandowski's style is more suited to (head coach) Pep Guardiola's style of football, while we also have Thomas Muller and Mario Gotze."
Bayern bought Mandzukic from Wolfsburg for a reported fee of €13 million in June 2012.
The 27-year-old has made 46 appearances for Croatia, scoring 13 goals at international level.
