The National Union of Professional Footballers [UNFP] backed Neymar and also hit out at what it claims is a "spiteful'' and "petty'' complaint from Barcelona.
A statement on the UNFP website read: "The UNFP fully supports the Brazilian player and would not hesitate to promulgate advice if Paris St Germain asked him to do so.
"Let the player express his talent on the field, as he did on the third weekend of Ligue 1, rather than want to send him to court in vile vengeance.''
Neymar plans to fight a claim by Barcelona for compensation following his move to Paris Saint-Germain, and has also promised to battle his old club for part of his 2016 contract renewal premium which he claims has not been paid.
Neymar left Camp Nou this month in a world-record €222 million deal, but Barca said on Tuesday they were pursuing €8.5 million in damages from the 25-year-old for what they allege to be a "breach of contract."
Neymar's response is the latest move in an increasingly bitter war of words following his move to France.
Despite his continuing troubles with Barcelona, however, life as a PSG player has started well for Neymar, who scored on his debut and then added two more along with three assists in a stunning display against Toulouse on Sunday.
Press Association contributed to this report.