The referee awarded a penalty to the Red Devils for handball by Presnel Kimpembe in the final moments of the game, and Marcus Rashford converted the spot-kick to eliminate the Ligue 1 champions from the competition.
The PSG star took to Instagram to hit back at the decision against his team following a handball VAR review during their Champions League last-16 clash.
Uefa has launched an investigation into Neymar's angry comments about the penalty awarded to Manchester United in their Champions League victory over Paris St Germain. "They get four guys who don't understand football to watch a slow motion replay in front of the TV".
Neymar watched last Wednesday's match from the stands, having returned from Brazil where he had been recovering from a second fractured fifth metatarsal in his right foot.
"It's a disgrace", Neymar had said in his Instagram post in Portuguese.
Following the comments, UEFA have now announced that they have opened proceedings on the Brazilian worldwide, with an outcome expected to be reached soon.
UEFA says it "appointed an ethics and disciplinary Inspector to conduct an investigation" of the social media comments.
Neymar was watching injured as United overturned a 2-0 first-leg deficit.