Neuer had injured his left foot in April and only recently made his comeback before fracturing the same foot again in a training session on Monday.
The 31-year-old, who captains both club Bayern Munich and country Germany, is widely regarded as the best goalkeeper in world football and his absence will be keenly felt by his club considering they have a busy fixture list up ahead.
The 6’4 custodian will miss all their remaining UEFA Champions League group-stage games, including the crucial double-legged ties against Paris Saint-Germain and at least 12 Bundesliga games.
The next international break in October sees Germany take on Northern Ireland and Azerbaijan for their World Cup qualifiers and while Die Mannschaft have already qualified, they will be seeking to confirm top-spot in their group.
Bayern host Bayer Leverkusen after the customary winter break and Neuer will be a contender to feature for the tie at the at the Allianz Arena on January 13.
In his absence, Sven Ulreich (Bayern) and Marc-Andre ter Steven (Germany) are expected to start for their respective teams.