Manchester United have secured Marouane Fellaini to a lengthened contract at Old Trafford after triggering the club's option of a 12-month extension to his current deal.

Senior figures at United and sources close to the player have confirmed to ESPN FC that Fellaini, a £27.5 million signing from Everton in August 2013, signed the contract last month after being reassured by manager Jose Mourinho that he remained an important figure in his plans.

As reported by ESPN FC, Mourinho had made it clear to Fellaini and the United hierarchy that he would not entertain offers for the 29-year, who scored the club's second goal in Tuesday's 2-0 EFL Cup semifinal first-leg victory over Hull City at Old Trafford.

But with Fellaini signing a four-year contract in 2013, with the option of a further year, the club confirmed to the player and his representatives in early December that they would be taking up their option to extend the contract until June 2018.

Fellaini has overcome negativity from supporters in order to secure his place in Mourinho's squad, with the Belgian midfielder hugging his manager on the touchline following his goal against Hull to give a visible signal of his respect for the Portuguese coach.

Fellaini has been the subject of criticism this season. OLI SCARFF/AFP/Getty Images

With Morgan Schneiderlin agreeing a £22m transfer to Everton and United open to offers for former Bayern Munich and Germany captain Bastian Schweinsteiger, Fellaini's importance to Mourinho is unlikely to diminish this season.

But with United pursuing Monaco's 22-year-old midfielder Tiemoue Bakayoko, Fellaini's long-term prospects may be under threat if the club can complete a deal for the France under-21 international.

Sources close to Fellaini have insisted that the player is determined to remain at United beyond his contract extension, but the club's move to trigger their option may ultimately be a move designed at protecting the value of their asset and avoid the risk of losing the player as a free agent at the end of this season.