Manchester United have "agreed" to sell midfielder Marouane Fellaini to Turkish club Besiktas for £8m ($11m) in the January transfer window, according to reports.

The Sunday Mirror claims the 29-year-old will be the first out the exit door at Old Trafford in January, after manager Jose Mourinho was instructed by the club's owners to sell players before making further additions to the squad.

The development comes as a surprise given the high praise Mourinho has often lavished on Fellaini, who joined United from Everton for £27.5m in 2013.

The 29-year-old is in the final 12 months of his Old Trafford contract and will be free to speak to other clubs from January.

Mourinho said last month that he was "worried" over Fellaini's future and has described him in the past as a key player in his squad.

"Marouane is just the fact I think he has important qualities and I try to use these qualities depending on the situation, depending on the team's needs," the Red Devils boss had said back in September.

Marouane Fellaini
Marouane Fellaini joined Manchester United from Everton for £27.5m in 2013 Getty Images

"He's a team player, a great character, we have a good relation and things are going really well between us.

"I think only a strong character would resist the difficulties here because he had some difficult times where people didn't recognise his qualities, where probably other managers didn't like so much the qualities that he has, so you have to be a strong character.

"He's a fighter, a guy with lots of pride. I'm really pleased I helped him to reach this and to change the perception the fans have now. I'm really happy for him."

Fellaini returned from a one-month knee injury layoff to play as a substitute in United's 1-0 defeat at Chelsea on 5 November – just 24 hours after he returned to full training.

The Mirror says Mourinho could move for Shakhtar Donetsk's Brazilian midfielder Fred as a replacement for Fellaini.