PSG said in a statement that the 26-year-old Neymar, who left the field in tears after suffering the injury in a French Cup game against Strasbourg on January 23, will not have surgery after the club consulted "world renowned experts" on Tuesday.
That means he will not be available when PSG visit united on February 12 or for the return last-16 Champions League clash at the Parc des Prince on March 6.
Paris Saint-Germain have made a last-minute move for Mesut Ozil but the German has told them he does not want to leave Arsenal on loan, according to reports in his homeland.
If that is the case, he could be back for the second leg of a potential Champions League quarterfinal, but along with matches against Manchester United he will miss Lyon away and Marseille at home in Ligue 1.
PSG expect the Brazilian to miss the next 10 weeks and Thomas Tuchel is desperate for cover, with German newspaper Suddeutsche Zeitung claiming they have approached Ozil.
An operation would have put Neymar's participation in that tournament at risk, as well as effectively ending his club season.
Neymar damaged the same foot towards the end of last season and battled to be fit for Brazil's World Cup campaign in Russian Federation, where he looked short of fitness during the group stages.
They added: 'The Brazilian global was in total agreement with the treatment plan'. Although he recovered in time for the World Cup, he was not at his best in Russian Federation.
"The club took control of the matter", a source close to PSG told AFP.
Still, it won't be easy for the Parisians against high-flying United sans the 26-year-old, not with the Red Devils on a 8W-0L-1D run since Ole Gunnar Solskjaer replaced Jose Mourinho as manager last month.
His injury comes just as the Ligue 1 leaders are also sweating on the fitness of key midfielder Marco Verratti, who has an ankle problem.