Italian media are reporting Michael Essien did not pass his Milan medical, so could be sent back to Chelsea.
According to La Repubblica, the 31-year-old Ghana international failed tests related to an old knee injury, having ruptured the anterior cruciate ligament twice.
Essien arrived in Milan on Friday evening and had his medical on Saturday morning, but so far has still not signed the contract.
This suggests there are problems and the Rossoneri could pull out of the deal.
He will undergo further stress tests at the Milan Lab in a bid to rescue the transfer, which would’ve been free for the club.
It would be a heavy blow for the club, who already sent Antonio Nocerino on loan to West Ham in order to make way for Essien.