Brazil's Neymar takes part in a training session in Teresopolis, Brazil on May 26 ahead of the Copa America. Photo: IC

With Paris Saint-Germain reportedly ready to listen to offers for Neymar while Paul Pogba has publicly declared that he wants a "new challenge" away from Manchester United, the summer transfer window in Europe could see considerable upheaval at several of the continent's biggest clubs.

PSG's ongoing quest for Champions League success has seen them bring back former sporting director Leonardo, and one of the Brazilian's first jobs could be trying to find a buyer for his compatriot, two years after PSG signed Neymar for a world record fee of 222 million euros ($264 million).

On Monday, sports daily L'Equipe reported that PSG "would not stand in the way of him departing" and added that Neymar "also sees his future away from Paris."

Agent Pini Zahavi, involved in the deal that brought the Brazilian to the French capital from Barcelona, is said to be actively trying to do a deal to take the player back to Spain.

Neymar's two years at the Parc des Princes have been marred by injury and contoversy and he is currently again sidelined by an ankle problem while also dealing with rape allegations.

PSG president Nasser al-Khelaifi appeared to target Neymar when he indicated that the club's highly paid stars would have to shape up or ship out in an interview with France Football magazine.

"They are not here to please themselves and if they do not agree, the doors are open. I do not want to have celebrity behaviour anymore," he said.

Perhaps Al-Khelaifi was also talking about Kylian Mbappe, PSG's other superstar forward who last month dropped a bombshell when he hinted he might be open to a new challenge elsewhere as he picked up the Ligue 1 player of the year award.

Real Madrid fans even chanted Mbappe's name at the unveiling of Eden Hazard last week, following the Belgian's 100 million euro move from Chelsea.

But with Real already having splashed around 300 million euros in the market, can they really afford a move for Neymar or Mbappe too? Meanwhile, coach Zinedine Zidane is believed to be most keen on completing a move for his compatriot Pogba.

Ideally, United want to keep one of their few world-class talents, even if Pogba's performances have often fallen well short of expectations since his then world record 89 million pound ($112 million) signing three years ago.

However, the Red Devils must now decide whether it is worth the risk to keep the Frenchman against his will or cash in to fund a rebuild.

United cannot offer Pogba Champions League football next season, and much is likely to depend on what offers come their way. Madrid and Juventus have been linked, but neither are likely to come close to the reported 150 million pound asking price.

Raiola back in the game

Potential suitors may also be warned off by the cost of dealing with Pogba's agent, Mino Raiola.

Pogba's statement to reporters of his intention to seek pastures new on a promotional tour in Tokyo on Sunday came just days after Raiola saw a three-month ban from brokering deals lifted by FIFA.

Raiola creamed off a reported 41 million pounds from the deal that brought Pogba back to Manchester in 2016.

With a season of Europa League football on the horizon and a huge rebuild needed at Old Trafford just to compete with Premier League champions Manchester City and Champions League winners Liverpool, Pogba clearly believes he can do better elsewhere.

"United should not be in a position where any player, let alone an underperforming one, feels that he can call the shots. That, though, is where the past six years appear to have left them," wrote The Times.

After also being burned in big-money deals for Alexis Sanchez and Romelu ­Lukaku, United seem keen to avoid getting in an arms race to replace Pogba should he go, even if the opportunity presents itself in what is expected to be a frantic summer of transfer activity.

Antoine Griezmann has announced his intention to leave Atletico Madrid but already seems set for Barcelona.

United have also played down interest in bringing Gareth Bale back to the Premier League from Madrid and seem set to be outbid by PSG to land another Raiola client in Ajax captain Matthijs de Ligt.

Manager Ole Gunnar Solskjaer has instead prioritized young and hungry recruits for United, and Welsh winger Daniel James, 21, has already been snapped up from Swansea City.