Manchester United fear Nemanja Matic injury as Jose Mourinho reveals key midfielder suffered 'muscular' problem against Watford

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Jose Mourinho revealed Nemanja Matic suffered a 'muscular' injury against Watford and fears that it is 'important'.

Matic, who has become a key member of Mourinho's midfield since his £40million summer move from Chelsea, was substituted after just 54 minutes in Tuesday's 4-2 win at Vicarage Road.

Mourinho admitted United were destabilised after Matic was forced off - they slipped from 3-0 up to a narrow 3-2 advantage before Jesse Lingard's stunning late goal sealed the victory.

Manchester United midfielder Nemanja Matic (centre) was injured in the win at Watford

Jose Mourinho showed concern on the touchline as his midfield enforcer left the pitch

The club are awaiting further news on Matic's condition ahead of Saturday's trip to old rivals Arsenal.

'Matic is injured, I don't know how badly,' said Mourinho. 'For Matic to tell me he wants to be replaced, he does not do that if it is nothing important. It is muscular.

'We lost stability when Nemanja Matic had to come out but the important thing is the three points.' 

Matic has become a key member of United's midfield since joining from Chelsea in the summer

Mourinho also spoke about Anthony Martial's fitness and revealed that he believes the Frenchman is not yet strong enough to cope with playing multiple matches in succession.

Martial, 21, scored United's third goal in the 32nd minute during a superb first half for United, but was withdrawn after 65 minutes for Marcus Rashford. 

'I think he suffers a little bit with accumulation of matches,' Mourinho told United's official website when asked about Martial's contribution. 'I could feel that in the second half he was going down and down and down.

'He’s still a young guy and his body, his biological situation has space to improve but in the first half, during the time, he had strength and explosion in his legs. He was dangerous and [scored] an important goal.'