Cape Town - Manchester United are sweating on the fitness of Nemanja Matic after the midfielder was forced off during the win at Watford.
Matic was substituted early in the second half at Vicarage Road with what Jose Mourinho labelled a “muscular injury”.
United will assess the damage to the £40million summer signing in the coming days, yet Mourinho clearly fears that the former Chelsea man could be set for a spell on the treatment table.
"For Matic to tell me he wants to be replaced, he does not do that if it is nothing important. It is muscular,” said Mourinho.
"We lost stability when Nemanja Matic had to come out but the important thing is the three points."
United were leading 3-0 when Matic went off after first half goals from Ashley Young (two) and Anthony Martial.
But after Mourinho’s men wasted several chances to extend their advantage, Watford gave them a scare by cutting the deficit to 3-2, before Jesse Lingard’s superb individual goal sealed victory for the visitors.
"We had chances for four, five and six in the first half and in the second half again and again and we didn't score," said Mourinho.
"So I think the players had the feeling that it was too easy, that the game was over and they [Watford] had no conditions to react.
"But then they reacted, they scored the penalty and it gave them belief. This team in mid-table have quality and they have no pressure that teams with other objectives have so they had no problems to concede four, five, six so when they scored two goals they gave a few minutes of everything when they believed anything could happen.
"It's a good lesson and it's good to have lessons without losing points. Maybe next time we are winning 2-0 or 3-0 the players will remember."