I would recommend to Pep (1) that as a bare minimum (alongside keeping Sane), he needs to get Digne (To address their LB issues once & for all), Koulibaly & Škriniar (To replace Kompany & Otamendi), De Jong (If Fernandinho is leaving after this season), Fabian (To replace David Silva), Sancho (To allow B.Silva to move into CM) & Kane (To replace Aguero). The only problem is that I also want most of those players to come to Old Trafford as well.
So if the Glazers did actually have a brain, United could easily catch up with City by getting these 7 instead.
(1) One should remember that City don't have FFP to deal with Next Season, considering that UEFA have de facto suspended it.