Tactics 4-2-3-1 and 3-4-1-2 are too different and you need to have a very large list of players to switch freely between them, do not agree with those who wrote that 3-4-1-2 defensive tactics. We need to finally decide and act on the transfer market based on one of them, and I hope it will be 3-4-1-2, even with such losers as Fred and Matic in the starting lineup it works great, today's match against Tottenham should prove it once again. Besides, we don't have any problems with the selection of players on offense and the defense looks very solid when we use it. Our transfer budget I would focus on buying two central midfielders, one deep lying playmaker and one box-to-box, with all due respect Fred and Matic it is not serious for a team that claims to be top 4, Ndidi (McTominay)-Pogba (van de Beek), in addition, if Bruno is injured then Pogba can always take his place Bruno(Pogba).
From not expensive variants it is really Kalvin Phillips and also I like the captain of AZ Alkmaar - Teun Koopmeiners, I recommend to look at reviews of his game on a Youtube, but nevertheless they do not approach that MU has made a quality bump in a class, and for Fred it will be possible in this window to rescue not bad money on the transfer markets, but to landing it hardly will happen.