The French champions have confirmed that the Brazil international is sidelined with a broken metatarsal and will be out of action for around 10 weeks.
Neymar will not undergo surgery but will now miss a significant part of PSG’s bid to win the Champions League.
United host PSG at Old Trafford in the first leg of their Champions League last-16 tie on February 12 before travelling to France for the return leg on March 6.
Should PSG beat Ole Gunnar Solskjaer’s side, it’s unlikely that Neymar will be available for their first quarter-final fixture, which would take place on either April 9 or 10.
Neymar has been in sublime form for PSG this season with 20 goals in 23 appearances. Elsewhere, the French champions have been given a boost ahead of their clash with United as RMC reported that Marco Verratti is due to return to training this week.
The Italy international suffered an ankle injury earlier this month and was a major doubt to be fit in time for the fixture against United. But Verratti has recovered quicker than expected and is expected to return for PSG’s clash with Bordeaux on February 9.