There's been a lot of speculation recently about who Jose Mourinho's fourth summer signing will be at Manchester United.Having already captured Romelu Lukaku, Nemanja Matic and Victor Lindelof for approximately £150 million, the Portuguese has been on the lookout for one final addition.A new full-back is reportedly a top priority, while there are arguments to be made that United still need reinforcements at centre-back and in the wide areas.Anthony Martial and Marcus Rashford are capable of playing on the flanks but both are strikers by trade, while Juan Mata and Henrikh Mkhitaryan are more suited to playing centrally.As for Jesse Lingard - well, he may be a winger, but he's just not very good.United have been linked a number of world-class wide players this summer, including Gareth Bale and Ivan Perisic, yet nothing has materialised.This is despite both players coming close to joining - even Cristiano Ronaldo thought Bale was destined to leave Real Madrid for United at one point.The money is there for Mourinho to spend, but time and time again he's been left frustrated by the club's inability to push deals over the line.And according to the BBC's Simon Stone, he might have just given up altogether.In the tweet below, Stone explains that Mourinho's 'fourth man' could end up being Andreas Pereira, who recently returned to United from a loan spell at Granada.Pereira's time in Spain has helped him "mature", which prompted Mourinho to keep him for the upcoming season.

If Mourinho has decided to not make a fourth signing and settle for Pereira instead, he can expect some backlash from United fans.

The 54-year-old vowed to bring in four players this summer and while Pereira is an exciting young talent, United a need an out-and-out winger, which he is not.

Pereira has even admitted he would prefer to play centrally for Mourinho, saying recently: "I've come back and I feel calm, I feel stronger mentally and physically.

"I can play as a midfielder, as a winger, as a holding midfielder. I'll play wherever the manager plays me but my best position is as a [central] No.6, eight or 10."