MUNICH -- Jose Mourinho has warned Manchester United face a "difficult" season if executive vice-chairman Ed Woodward does not bring in new faces before the transfer deadline.
Sources have told ESPN FC that Bayern Munich's Jerome Boateng has moved up the list of targets as United look to secure a centre-back before Thursday's cut-off.
Speaking before United's 1-0 defeat to Bayern on Sunday night, the United manager admitted his concern for the coming campaign if his squad is not bolstered before the Premier League kicks off with Leicester's visit to Old Trafford on Friday.
"The other clubs that compete with us are really strong or they have already fantastic squads like Chelsea, Spurs, City, or they are investing massively like for example Liverpool buying everything and everybody," Mourinho told MUTV.
"If we don't make our team better it will be a difficult season for us.
"My CEO knows what I want for quite a long time, I know he tries to do the best for me and I still have a few days to wait to see what happens."
Mourinho wants two new players before Thursday's transfer deadline -- a centre-back and a right winger -- but has privately conceded one new arrival is more realistic.
Negotiations for Harry Maguire and Toby Alderweireld are becoming increasingly difficult, sources said, leaving Woodward to turn his attention to German defender Boateng, who is likely to cost in the region of £50 million.
Meanwhile, sources also confirmed earlier reports that Chelsea are willing to swap Willian for Anthony Martial, who did not travel to Germany for the friendly with Bayern Munich on Sunday.
The Frenchman instead stayed behind for a double training session at Carrington after leaving the tour of the U.S. to attend the birth of his child.
Mourinho, according to sources, is open to the idea of replacing Martial with Willian but Woodward has concerns about swapping the 22-year-old for the Brazilian, who will be 30 this month.
Martial has made it clear to Mourinho and United's board that he wants to leave Old Trafford this summer.
Mourinho, according to sources, does not want an unhappy player in his dressing room but Woodward is reluctant to part company with a young player who still has two years on his contract.