Paris Saint-Germain have appealed to the Court of Arbitration for Sport (CAS) to stop UEFA re-examining its decision to clear the club of breaching Financial Fair Play (FFP) regulations.
PSG, who in 2017 signed Neymar for a world-record €222 million and Kylian Mbappe on an initial loan before making the deal permanent for €180m, raised funds of around €50m through transfers at the request of UEFA to avoid sanctions for the 2015, 2016 and 2017 financial years.
Javier Pastore, Yuri Berchiche, Odsonne Eduoard and Jonathan Ikone were all sold by Thomas Tuchel's side in the summer.
A statement from CAS read: "The Court of Arbitration for Sport (CAS) has registered an appeal filed by the French club Paris Saint-Germain against a decision rendered by UEFA in September 2018.
"At the parties' request, the procedure will be conducted on a confidential basis with the exception of the final Award which will be published.
"In these circumstances, CAS is unable to provide any further information regarding the matter."
UEFA's initial sanction related to Milan's failure to fulfil the break-even requirement set out in the governing body's FFP regulations.
While CAS accepted this decision, rejecting the Rossoneri's request to force UEFA into a settlement agreement, it claimed the ban from Europe was not a proportionate punishment.