The defensive midfielder will play at center-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 for the Blaugrana, but will be given his role of 'false No. 9' when they take to Camp Nou.
In other news, Javier Mascherano, who has been regularly deployed in defense as a makeshift, will be paired alongside Sergio Busquets in the heart ofits backline, as Carles Puyol has failed to convince Pep Guardiola of a starting berth.
Other changes for the hosts include David Villa and Lionel Messi returning to the lineup as expected, in place of Alexis Sanchez and Cesc Fabregas, with the former tearing his hamstring in the 2-2 draw with Real Sociedad at the weekend, and the latter on the bench.
Meanwhile for Massimiliano Allegri's Milan side, it has made five changes from the team that also 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 lineups 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