The 27-year-old described referee Damir Skomina's late penalty decision, made after he reviewed the Video Assistant Referee (VAR) technology, as a "disgrace" on social media.
Marcus Rashford coolly fired the penalty into the net to send United through and PSG out of the competition as Neymar - who came to the touchline from his private box to celebrate with his team - raged about the decision.
UEFA, on Wednesday, said a disciplinary investigation has started after the PSG forward criticised in an Instagram post the officiating of the defeat to Manchester United.
If found guilty the 27-year-old risks being suspended during the early rounds of next year's Champions League, for which runaway Ligue 1 leaders PSG are certainties to qualify.
"They even put four people who don't understand football watching the incident in slow motion".
UEFA today confirmed they are launching an investigation into Neymar's comments via a statement on their website. How can it be a handball when it hits...
Neymar missed both legs of the tie after injuring his foot in January.
Neymar, who is now sidelined with a foot injury, had watched the game from the stands.
Westbrook not interested in revisiting fan drama
Westbrook took no questions from reporters about the incident (or the game), only delivering a 3-minute long statement. The NBA sent out a memo to all 30 teams asking them to create PSA's addressing the need for civility during games.