Manchester United could lose Marouane Fellaini for free next summer after the midfielder refused to sign the new contract the club offered him in September.

Negotiations have been under way since last season on a deal, with Fellaini unhappy at the terms offered. The Belgian is thought to earn around £120,000 a week after United triggered a one-year extension in January and raised his salary from £80,000 a week. He wants a marked increase on his terms.

Despite the stance, José Mourinho will not sanction the 29-year-old’s sale in the January window even if Fellaini has still not agreed a fresh deal by then. As the former Everton man is out of contract in the summer and United do no hold any options to trigger an automatic extension he would be free to sign a pre-contract agreement with any club outside the Premier League in January. Player contract regulations stipulate they can negotiate a transfer six months before their current agreement expires.

Fellaini has emerged as a key part of Mourinho’s team, after he endured a difficult start when signing for David Moyes for £27.5m in the summer of 2013. The Portuguese manager is intent that the midfielder should extend his stay at the club. Despite the protracted discussions and the impasse Mourinho has not given up hope Fellaini will agree to sign on again.

Yet if he does not do so then United face the prospect of a player who turns 30 next week, and so is in his prime, walking away for nothing.