The ex-Chelsea defender believes Barca's weakness isn't solved by adding the diminutive defender.
"He is an extremely well-rounded defender, and is quick and very smart," Ferrer said. "He gives the team balance, since he will open things up on the left flank.
"But there is a lack of height. They will probably struggle with crosses from free-kicks and corners, because their only tall players will be the two centre-backs and Sergio Busquets, but that is this Barca's style of play.
"The team spends most of its time on the attack and needs fast players who offer penetration. Having said that, if the full-backs push forward a lot, the rest will have to make sure they cover for them."