The midfielder takes up his usual spot in the Blaugrana midfield after recovering from a calf injury, with Alexandre Pato back in the Rossoneri squad
The Spain international midfielder had been a doubt earlier this week after picking up a calf injury, but has been named in the starting XI to take on the Italian side, who held the defending European champions to a 0-0 draw in last week's first leg.
Cesc Fabregas also starts after missing last Wednesday's clash at San Siro, with Seydou Keita dropping to the bench. Elsewhere, Isaac Cuenca is called up, with Alexis Sanchez starting as a substitute.
For Milan the big news is that Alexandre Pato is back in the 18 after returning from the USA, where he was treated for the persistent muscle injuries that have blighted him for the past three seasons. He starts from the bench, with Zlatan Ibrahimovic and Robinho once again leading the line from kick-off.
The clash gets underway at 20.45CET, with a score draw or away win enough to take the Italians through. A 0-0 draw would send the game into extra-time and potentially penalties in order to determine who will face either Chelsea or Benfica in the two-legged semi-final.
Barcelona (4-3-3): Valdes; Dani Alves, Pique, Mascherano, Puyol; Xavi, Busquets, Iniesta; Fabregas, Messi, Cuenca.
Subs: Pinto, Sanchez, Adriano, Thiago, Keita, Pedro, Tello.
AC Milan (4-3-1-2): Abbiati; Abate, Mexes, Nesta, Antonini; Nocerino, Ambrosini, Seedorf; Boateng; Ibrahimovic, Robinho.
Subs: Amelia, Yepes, Bonera, Aquilani, Emanuelson, Maxi Lopez, Pato.