The defensive midfielder will play at centre-back, alongside fellow makeshift defender Sergio Busquets for the hosts, whilst the visitors make multiple alterations to their side
The forward started on the substitutes bench at the weekend at Zaragoza, but will be given his role of 'false No. 9' when they take the field at Camp Nou.
Javier Mascherano, who has been regularly deployed in defence will be paired alongside Sergio Busquets in the heart of Barca's back line, as Carles Puyol has failed to convince Pep Guardiola of his fitness.
Another change for the hosts includes David Villa returning to the team as expected, in place of the injured Alexis Sanchez.
Meanwhile, Massimiliano Allegri's Milan side make five changes from the team that drew 2-2 with Lazio on Friday.
Gianluca Zambrotta, Antonio Nocerino, Mark van Bommel, Clarence Seedorf and Alexandre Pato all come into the fold, at the expense of Luca Antonini, Massimo Ambrosini, Gennaro Gattuso, Alberto Aquilani and Zlatan Ibrahimovic.
The line-ups are as follows:
Barcelona: Valdes, Alves, Mascherano, Busquets, Abidal; Keita, Xavi, Iniesta; Pedro, Messi, Villa.
Subs: Pinto, Puyol, Maxwell, Fabregas, Thiago, Afellay, Adriano.
AC Milan: Abbiati; Abate, Nesta, Silva, Zambrotta; Nocerino, van Bommel, Seedorf; Boateng; Pato, Cassano.
Subs: Amelia, Bonera, Yepes, Antonini, Aquilani, Ambrosini, Emanuelson.
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