News broke over the weekend that Sunderland were set to seal the signature of Methalie for a reported £25.6m deal, with the left-back travelling to Wearside to complete his medical this week.
It has since been reported by various outlets, including Sky Sports, that the Black Cats noticed a back issue in his medical results that has put any potential move on hold for the time being.
Methalie has returned to France for further tests, with Toulouse reportedly keen to see for themselves whether or not the issue is significant enough to change the deal the two clubs had in place.
The 20-year-old has been highly sought-after throughout the summer with reported interest from both Roma and Newcastle, yet the player was reportedly keen to join Regis Le Bris' Sunderland side - who are set to compete in the Europa League during the coming season.
A deal has not been called off completely, but it currently hangs in the balance with further medical examinations to take place.