It is a good investment for Manchester United, Diego León is a young talent and I think Manchester United needs to starting replacing the old squad with new young players. This signifies Manchester United aim in trying to build for the future. Chelsea made a lot of young signings last season and people laughed at them but look what the team now, they are playing well and winning games.
I do believe that Manchester United should include one or two new players and give them a chance to see how they fit in the team. The performance of them is on the decline and we are seeing this in this season where they have won only 5 matches in premier league and lost 6 matches. They aren't in the top 10 teams currently on the points standing and it is obviously against their standard. Also keep in mind, just bringing new blood in the team won't have an immediate effect but in the long run, it will be beneficial for the team.
Manchester united is one of those club that should not just be looking to sell just a few players but should necessarily do an overhaul of players if they are hoping to start becoming one of a relevant team in the league. even with the signing of a very good coach that looks like one that can bring them victory, they don't still look like a team you can bank on that they are back on track and that they have what it takes to do better than they are currently playing.
if they can make the hard decision of signing some few young and talented player that will spice things up for the team, maybe they might start to get good result, and things might start to fall into place. as for some experienced playing coming into the team that are already playing ion a top league, it will be difficult to see a player that is ready to join the team at the time it appears as though things is getting more difficult for them. it's going to be a long process before they will come out of this tough mess but what will make it faster will be the signing of some young talents that rare ready to give it all for the team.