The Germany goalkeeper suffered a fractured foot when Cristiano Ronaldo completed his hat-trick in extra time of Tuesday’s 4-2 Champions League defeat at the hands of Real Madrid.
Bayern already announced an initial diagnosis on Tuesday and Rummenigge has now revealed the 31-year-old will be out of action for an estimated two months.
“Neuer has suffered a serious injury,” the Bayern chairman told reporters.
“He will be out of action for eight weeks.”
Neuer had only recently returned from foot surgery in the first leg against Madrid, having missed three Bundesliga fixtures following a training incident last month.
His latest injury means Neuer will be unavailable for Bayern’s remaining five Bundesliga games as they defend an eight-point lead over second-placed RB Leipzig, while he will also miss next week’s DFB-Pokal semi-final against Borussia Dortmund.
Neuer’s absence will probably see Sven Ulreich return to the starting XI, with the 28-year-old also deputising for the former Schalke shot-stopper during his previous injury problem.