"A disciplinary investigation has been initiated based on Article 31(3) of the UEFA Disciplinary Regulations in connection with statements made by PSG player Neymar," UEFA said.
"Information in respect of this investigation will be made available in due course," it added in the statement.
United, who had lost the first leg at Old Trafford 2-0, were awarded a stoppage-time penalty for handball against Presnel Kimpembe after the referee consulted VAR.
Marcus Rashford held his nerve to score and seal a 3-1 victory for United which was enough for the visitors to progress on away goals after the tie ended 3-3 on aggregate.
Neymar missed both legs of the tie after injuring his foot in January.
(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Ken Ferris)
