I think any club that has not performed well in the present season and is not ready to spend good money on signing new players it will be hard on them in the coming season,
The way last season ended, am sure next season will be very competitive, most clubs should be prepared to sign quality player's before the next season is going to start, any club that thinks they performed well in the last season and they don't really need to update their squad before the next season start, they are going to perform poorly in the coming season, next season will be very competitive.
and this is a big sign of potential troubles for Manchester United because if they make the mistake of signing the wrong goalkeeper,
The worst thing that will happen to Manchester united is signing a wrong goal keeper, De Gea made some silly mistakes in the season that ended which really affected Manchester united, if they didn't sign a experienced goal keeper, then they are going to end the season in the position which they don't expect.
Considering his performance last season, I think David De Gea's time as the first choice goalkeeper of United is coming to an end and that's why the club needs to make sure they get a better replacement for the Spanish goalkeeper in this summer transfer window.
I think United's scout team must have tabled the name of some world class goalkeepers that are capable of taking over from De Gea. However, it is rumoured that the club has a current financial crises at the moment which why they won't be spending much on new players this summer