The French striker was stretchered off with an apparent serious head injury following a strong clash with Lyon's Anthony Lopes on Sunday.
PSG's doctors claimed after the game that it "wasn't too serious", but reports from the aforementioned source on Monday allege that Mbappe has suffered a cervical fissure in the brain which requires two months recovery.
However, even the player himself has reassured fans through social media about his physical condition: "It was more fear than harm despite the impressive shock".
It seems that the jury will remain out regarding the possible return of the Frenchman, with head injuries often taking time to heal.
Nonetheless, the Parisian club will be praying that he is back fit for their first Champions League fixture at the Bernabeu on 14th February.