The Brazilian sustained a metatarsal injury in his right foot during PSG's clash against Strasbourg in the Coupe de France round of 16 match on 23 January and he received a thorough examination at the club's training ground on Tuesday.
Following the review, Neymar has been ruled out of action for 10 weeks, which will see him miss a crucial run of fixtures for the French champions.
The mercurial forward will play no part in PSG's trip to Old Trafford on February 12, nor will he be available to play in the return leg at Parc des Princes on March 3.
A PSG statement said the club had gathered a group of "world-renowned medical experts" in order to come to this conclusion following an in-depth review of the problem.
"After detailed analysis by the specialists, a consensus was reached of a conservative treatment of Neymar Jr's injury to the fifth right metatarsal," it read.
"Informed of this recommendation, Paris Saint-Germain's Brazilian international striker agreed with this protocol. As a result, Neymar Jr is expected to return to the field within 10 weeks.
"Paris Saint-Germain sends its strongest support and encouragement to Neymar Jr to overcome this injury, with the courage and determination that the player has always shown."
Neymar suffered a similar foot injury last February that kept him out of the remainder of the 2017-18 season, including the second leg of the Champions League defeat to eventual winners Real Madrid.
He recovered in time to play for Brazil at the World Cup but was unable to inspire his country - widely tipped for success - to a sixth title.
This latest news will come as a huge blow to supporters and PSG boss Thomas Tuchel, given the fact that Neymar has had such a huge influence on their 2018-19 campaign so far.
The 26-year-old has scored 20 goals in 21 appearances across all competitions this season, helping PSG storm clear at the top of Ligue 1.
Neymar will now miss a number of crucial domestic games additionally, including the trip to Lyon this Saturday and another away clash against Saint Etienne on February 17.
Fortunately, PSG are already overwhelming favourites to retain their Ligue 1 crown, having established a 13-point lead at the top of the table ahead of Lille.
Depending on how Neymar's recovery goes, he might also have to sit out the Champions League quarter-finals if PSG get past United, with his expected return date not yet known for certain.