The French forward’s current deal with Mauricio Pochettino’s side expires at the end of the season, with no concrete indication that he has any intention of putting pen to paper on an extension.
Liverpool have been touted as admirers of the 23-year-old for a considerable while, as have Spanish giants Real Madrid.
But Real boss Carlo Ancelotti admitted earlier this month that his side were likely to wait until the summer to make their move for the player, opening a potential bidding war to secure a talent who would become one of the most highly sought after assets in world football.
And Wenger is of the opinion that the longer PSG wait to try and prevent Mbappe’s departure, the more difficult they will find the task at hand.
What has Arsene Wenger said about Kylian Mbappe?
"In my experience, when you try to renew a player then the longer it takes the more difficult it becomes.
"I've been waiting a year and a half for PSG to manage to renew Mbappe. He is the most indispensable player in PSG's way of playing. But, there is little time left and today the footballer is free to sign wherever he wants.”
Wenger also made reference to a previous Real approach for the striker.
He added: "PSG were in a situation where they had a firm offer from Real Madrid. When you reject 180 million euros, even for PSG it still is a huge sum.
"So, when they refused this money, they either said to themselves 'We need to have a great season, as we have [Lionel] Messi and we can't afford to lose Mbappe' or they thought 'we will manage to convince him to stay'."