MUNICH, Germany -- Manchester United are stepping up their attempts to sign Jerome Boateng from Bayern Munich, sources have told ESPN FC.

Jose Mourinho is desperate to sign a centre-back before Thursday's transfer deadline and with potential deals for Harry Maguire and Toby Alderweireld not coming off, United have turned their attention to the Germany international.

Mourinho warned on Sunday he faces a "difficult" season if executive vice-chairman Ed Woodward cannot add to the squad before the first game of the season against Leicester on Friday.

He wants a central defender and a right winger but is willing to accept just one new arrival.

Sources have told ESPN FC that Boateng, who played 45 minutes against United on Sunday, wants to leave Bayern this summer after seven years at the Allianz Arena.

The German champions are open to offers but want a fee in the region of £50 million. Sources have told ESPN FC United are hopeful of negotiating that down.

Woodward has so far refused to meet asking prices for Maguire or Alderweireld and Boateng, who will be 30 next month, is considered to be a more straightforward deal.

The defender, who spent one season at Manchester City, has also been linked with Paris Saint-Germain but sources have told ESPN FC the French side are yet to make a formal bid.

Jerome Boateng in preseason action for Bayern Munich. Photo credit should read CHRISTOF STACHE/AFP/Getty Images

Should Boateng arrive, it is likely to signal the end of Marcos Rojo's time at Old Trafford.

The Argentina international has been linked with a £30m move to Everton and did not travel to Munich with the rest of the squad on Sunday.

Anthony Martial's future is also uncertain after he also failed to make the trip to Germany.

He returned to training on Friday after leaving the tour of the United States and missing a week while he attended the birth of his son in Paris.

Sources have told ESPN FC that instead of facing Bayern he was asked to undertake a double training session at Carrington.

Marcus Rashford, who was not part of the squad on the U.S. tour, also returned to training on Friday but was deemed fit enough to start the 1-0 defeat to Bayern.

Sources have told ESPN FC that Mourinho will allow Martial to leave but Woodward is more reluctant to part company with a player who is only 22 and still has two years left on his contract.

Bayern, according to a source, are not interested in Martial while PSG are more likely to bid next summer. Juventus have also cooled their interest following the arrival of Cristiano Ronaldo from Real Madrid.

Chelsea are interested and could offer Willian, 29, as bait -- a deal that would appeal to Mourinho even if it meant Martial signing for another Premier League club.