Sunderland looked to have completed Dayann Methalie's signing from Toulouse, but there's been a last minute twist.

Weeks of talks appeared to have produced the breakthrough Regis Le Bris wanted, with the Black Cats moving decisively for one of Ligue 1’s most highly rated young full-backs.

The negotiations had been anything but straightforward.

Toulouse stood firm over their valuation while Sunderland gradually improved their offer, refusing to walk away from a player identified as a major target.

Fabrizio Romano eventually reported that the clubs had settled on a package worth £24 million up front, with another £1.5m available through bonuses.

Methalie was expected to sign a five-year contract after travelling to the North East. The language surrounding the move was confident, with media sources describing it as a done deal and reporting that the paperwork was being signed.

At that stage, only the usual final checks appeared to stand between Sunderland and another solid addition.

The 20-year-old made 27 Ligue 1 appearances for Toulouse last season, scoring twice and supplying one assist. Although primarily a left-back, he can operate as a wing-back or on the left of central defence, giving Le Bris valuable tactical freedom across a demanding domestic and European schedule.

Methalie’s pace, height and ability to carry the ball made him an attractive long-term option. He could have competed immediately with Reinildo while being developed into Sunderland’s first-choice defender on that flank.

His arrival also would have strengthened a vastly French-speaking dressing room already familiar with Le Bris’s methods.

However, the transfer has now taken a dramatic and potentially decisive turn.

Sunderland deal for Dayann Methalie now 'in jeopardy' after last minute twist

Sky Switzerland's Sacha Tavolieri reports that Sunderland’s staff identified concerns relating to Methalie’s physical condition during his medical.

The proposed signing is consequently in serious doubt, and the France Under-21 international has travelled back home instead of being unveiled on Wearside.

The development has also reportedly created tension with Toulouse, particularly after the clubs only found agreement at the end of a long negotiation.

A medical concern doesn't automatically mean the transfer is finished.

Clubs can request more tests, renegotiate the financial structure or introduce clauses offering protection against a future problem.

Sunderland must now decide whether the warning is manageable or whether completing this expensive deal for a youngster would carry too much risk.

There has been no official announcement that the move has collapsed. Both outcomes therefore remain possible, but the timing could hardly be worse with the Premier League campaign about to begin.

What seemed certain only hours ago is now hanging in the balance.