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Manchester United have given Jose Mourinho the green light to aggressively strengthen the English Premier League club's defence in the winter transfer window.

Mourinho has prioritised the addition of a Champions League -level central defender to his squad in January.

According to club sources, Manchester United executive vice-chairman Ed Woodward is prepared to allocate significant funds to the transfer fee and salary.

The Portuguese manager made one addition to United's defence in his first window at Old Trafford, recruiting Eric Bailly from Villarreal for an initial €35million fee.

The 22-year-old was an ever present until he damaged a collateral knee ligament in October's loss at Chelsea.

(Image: Manchester United/Getty Images)

Though Mourinho advised his new club to sign a second central defender and full back in the summer window, neither reinforcement was secured as Woodward and his staff failed to make space in United's squad by moving out any of a group of senior professionals deemed surplus to requirements.

Forced to operate with a squad in which his most experienced defender Chris Smalling had less than 150 league appearances, Mourinho subsequently suffered a series of rearguard lapses wholly uncharacteristic of his coaching philosophy.

Individual errors have cost United a number of early or decisive goals and points, keeping just seven clean sheets in 22 matches.

Four of those clean sheets came with Bailly in the starting line up. Though the Cote d'Ivoire international is close to a return to first-team duty, he expects to be lost to Mourinho again in January when called up for the Africa Cup of Nations in Gabon.

(Image: Getty Images)

Should the 2015 winners reach the knock-out rounds, Bailly will be absent until February.

United's decision to invest in their defence is a demonstration of the board's faith in their new manager amidst hysterical external criticism of Mourinho's results and behaviour.

While a series of home draws has left United eleven points behind leaders Chelsea, Mourinho's characteristic - and unfashionable - refusal to 'dump' participation in either the League Cup and Europa League last night left him as the only Premier League manager still competing for silverware on four fronts.

United won the Community Shield in August, and on Wednesday defeated West Ham United 4-1 to secure a League Cup semi-final tie with Hull City. Mourinho won the competition three times in his six attempts as Chelsea manager, and is yet to lose a League Cup tie in normal time.