Marcus Rashford scored the spot-kick to give United a 3-1 win on the night and send them through on away goals.
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.More news: Johnson & Johnson to pay $42m in baby powder cancer payout
UEFA says it "appointed an ethics and disciplinary Inspector to conduct an investigation" of the social media comments. "They put 4 people that know nothing about football in charge of looking at the replay for VAR".
Nyon: UEFA have opened disciplinary proceedings on Neymar after his foul-mouthed outburst about referees following Paris Saint-Germain's controversial Champions League exit to Manchester United last week, the governing body announced on Wednesday.More news: Pi Day 2019 deals in Hampton Roads
Following the comments, UEFA have now announced that they have opened proceedings on the Brazilian worldwide, with an outcome expected to be reached soon.
Neymar, meanwhile, has not featured for PSG since he went off injured in the side's 2-0 victory over Strasbourg on January 23.More news: Man blocks arrow fired at him with mobile phone