Paris Saint-Germain will go backwards if Kylian Mbappe leaves for free, according to former midfielder Jerome Rothen. 

Mbappe's contract is due to expire at the end of the season and he has been heavily linked with a free transfer to Real Madrid, whose president Florentino Perez this month said he would have news about the 22-year-old in January. 

The World Cup-winning attacker has scored 138 goals and supplied 62 assists in 184 appearances since joining PSG in 2017, developing into one of the most exciting talents in world football. 

He scored the opening goal in the 3-2 Champions League win over RB Leipzig on Tuesday but blazed a penalty over in second-half stoppage time following a Lionel Messi double.

Still, Rothen believes it is Mbappe, not Messi or Neymar, who is essential to PSG's future.

Their win percentage in all competitions drops by 5.7 per cent to 69.8 per cent when Mbappe does not feature, while their average goals scored slips from 2.7 to 2.3 in his absence. 

"If Mbappe leaves for free, PSG will go backwards I am sure," Rothen said on RMC Sport. 

"It's a chance to have one of the best players in the world. He is the player who best represents Paris Saint-Germain today, the player who often makes the difference and makes you win the big games. 

"It must be shown to Mbappe and his entourage, that the project is around Mbappe, not anyone else. It's not around Lionel Messi or Neymar. 

"Of course, Lionel Messi remains Lionel Messi. Except that today, we see he can disappear for 20 or 30 minutes." 

Mbappe revealed this month that he asked to leave PSG in the close season so they could get money from selling him and find a replacement. 

Messi has a contract at the Parc des Princes until June 2023, with the option for another year, while Neymar's deal runs until 2025.