The decision was on PSG and Mbappe itself. The club can put him on the transfer market. I think that it will far better for PSG to sell him this season rather than waiting for his contract to end next year.
PSG will get nothing if mbappe will be leaving from the club with a free agent. It seems like that manchester united is having very big ambition to sign mbappe. MU has even prepared an exchange deal for mbappe.
I think that this gonna be a very important season for PSG and mbappe. I saw that if all of players in PSG are not willing to see mbappe to leave from the club. I think that's mbappe's strategy caused by he knew that if PSG will put very big release clause for him.
Now PSG is at a very confusing point, management must be able to respect Mbappe's decision but on the other hand, if PSG don't sell him as soon as possible then they won't be able to get anything for his departure next season. We know that PSG has spent a lot of money on his salary but still cannot achieve the team's goals, therefore the management definitely doesn't want his departure on a free transfer to happen. The only solution is to sell it this season to at least make up for the money that has been spent. Manchester United is one of the teams expecting Mbappe to arrive, they are ready financially. But I think it will be better if Mbappe goes to Real Madrid because Real Madrid is his dream team and he will have a great chance to get some UCL trophies. It would be a loss if Mbappe chose to join Manchester United because it is unlikely that he will be able to achieve various new achievements. I hope Mbappe knows what he has to do to advance his career in the future.
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The only way to let him stay even longer or terminate his contract. Just put him in the bench will be enough. I think that if mbappe will be threatened not to play in upcoming season and he will think for twice to stay even longer in PSG.
PSG will be on very big disadvantage if he stays even longer caused by PSG will lose ability to sell him for big money.
However, in any case, in my opinion, PSG should immediately open a sales window for him, Mbappe wants to stay until the end of his contract, and if PSG agrees then they will get nothing and obviously this can be a big loss for the team.