#4: Nelson Semedo
Dani Alves left a significant hole down Barcelona's right-side of defence after leaving to join Serie A champions Juventus last summer.
Interestingly, they decided against signing another full-back. Instead, they placed their confidence in both Sergi Roberto and Aleix Vidal. For a number of reasons though, neither of the two were able to consistently match expectations within their backline and Barcelona's defensive weaknesses were exploited.
Roberto, predominantly a defensive-minded midfielder, utilised his versatility to play at right-back but struggled against tougher opposition. Questions have been continually asked about Vidal meanwhile, who at 28, doesn't instil team-mates with much confidence and many feel he's just not good enough quality to warrant a starting place at Barcelona.
Having suffered heavy defeats at the hands of both PSG and Juve, a quarter-final exit from the UEFA Champions League was seen as the exclamation point during a forgettable campaign.
However, they seem to have filled Alves' void well on this occasion. By acquiring Benfica's Nelson Semedo this past summer, the defender has settled quickly and used his attributes well to justify why they were prepared to part with a reported £26m for his services.
Solid defensively, calm in possession, intelligent and deceptively strong, the 24-year-old's ability to link-up play with team-mates and create attacking opportunities too is exciting to watch.
They cannot afford to drop the Portuguese international ,not least while he's in such a rich vein of form.