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Francesco Acerbi was acquired from Chievo last summer after impressing for the Flying Donkeys, but he has done nothing that reminds you of the player that Milan thought they were signing.
He is just 24 years old, so perhaps there is room to grow as a player and eventually become good enough to represent a top club, but that time is not now, and Allegri should resist using him any further this season.
Acerbi appeared to be a clown at the back when Giovinco ran at him or left him for dead with his movement and change of direction.
It was a terrible partnership that he formed with Philippe Mexes, who was typically rash in the tackle and tended to lunge for the ball and jeopardise his team's ability to hold up Juve in transition.
A typical example of how poor the pair of them worked together was the Mirko Vucinic winner in extra time.
The French centre-back came across to the right as Emanuele Giaccherini shifted the ball into the path of Paolo De Ceglie and Vucinic, who were bombing forward.
Ignazio Abate should not be excused either, as the Zenit target failed to cover adequately, but Mexes lunged in to deny De Ceglie and completely missed the ball, leaving Vucinic in the clear.
Acerbi was nowhere near the Montenegrin—his reaction to the events unfolding and ability to cover yet another example of his ineptness—which provided the Juve striker with the simple task of slotting past Marco Amelia.
With Daniele Bonera, Mario Yepes and Cristian Zapata sidelined, the Rossoneri are in desperate need of a new centre-back, as these other options are also short of the required quality to move Milan into contention for a Champions League place for next season.