Mourinho warned in the summer that his side faced “a difficult season” if they did not strengthen before the transfer window closed.
Manchester United chiefs are concerned at the confrontational approach taken by the Portuguese, although he retains the full backing of the board.
Senior officials are convinced that executive vice-chairman Ed Woodward is in full control of the situation, despite fears that if it’s not tackled quickly then a snowball effect could occur.
He had highlighted his team’s defence as an area that needed bolstering, but deadline day passed without any new arrivals.
United were linked with several defenders during the close season, including Leicester’s Harry Maguire, Tottenham’s Toby Alderweireld and Bayern Munich’s Jerome Boateng.
Pogba’s second stay at United is seemingly in jeopardy due to a rift with manager Jose Mourinho.That said, there is little panic among the club’s top brass and Mourinho has now moved to solve the unrest in his dressing room.