Neymar was due to arrive at the French champions’ training ground on Monday but was absent without leave, which fuelled speculation that he is weighing up a return to his former club Barcelona.
A club statement revealed: "PSG affirms that the player Neymar Jr was not present at the time and place required, without prior authorisation from the club. PSG regrets this situation and will take appropriate action."
PSG sporting director Leonardo revealed the club will not stand in Neymar’s way if the Paris club receive a good offer for the player they signed from Barcelona for £220m in 2017.
"Neymar can leave PSG, if there is an offer which suits everyone,” Leonardo told Le Parisien. “But up to now, we do not know if anyone wants to buy him, or at what price. It will not be done in a day, that's for sure.
"PSG want to count on players who want to be here and build something big. We do not need players who are doing a favour to the club by being here."
Leonardo added that the club will follow an "internal procedure" and "consider the measures to be taken" regarding his absence from training.
Neymar was brought to Paris in 2017 to help them achieve their ultimate aim of winning the Champions League, but a series of injuries and disappointing runs in the competition has left the club wondering whether he is worth the hassle.
Barcelona president Josep Maria Bartomue recently said that he understood Neymar was keen to return but was unsure whether the player was for sale.
Leonardo admitted PSG have had "superficial" contact with Bartomeu about a move for Neymar, who has three years remaining on his contract.
"Only one thing is certain today: he is under contract with us for three years. And since we have not received an offer, there is nothing to discuss.
"We have not received any offers. But we have had, it is true, superficial contact (with Barcelona).
"They said they want to buy him but that we are not selling. It was (Bartomeu) who said that. But we have not seen that Barcelona are truly in a position to buy him.
"A move of this magnitude is not just a question of emotions. It is a financial question.”
Neymar missed the Copa America tournament - which Brazil won by beating Peru 3-1 in Sunday's final - due to an ankle injury sustained in a friendly against Qatar last month.
He is banned for three matches at the start of the new Ligue 1 season after lashing out at a fan at the end of PSG's shock French Cup final defeat to Rennes in April.
The former Santos forward will also miss his next three European matches after insulting match officials at the end of his side's Champions League defeat to Manchester United in March.
Additional reporting by PA
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