CDM: Sergio Busquets

Sergio Busquets may be 30 now, but he's still as good as he was under Pep Guardiola and Luis Enrique.
He's been one of Barcelona's stand-out players this season alongside Messi. It's a bit cruel to leave Casemiro out because the Brazilian's been pretty decent as well, but Busquets is easily the best holding midfielder in the world right now.
Real Madrid may be struggling to get goals, but El Clasico always brings out the best in both teams. Busquets will have to be on his toes for the entire 90 minutes.
Central Midfielder: Toni Kroos

Following a severely disappointing World Cup in Russia, Toni Kroos is back to what he does best for Real Madrid.
The German has an incredible 94.4% passing accuracy in LaLiga this season. Real may be struggling on the front foot, but Kroos has kept the midfield ticking.
His error in the Champions League tie against CSKA Moscow led to a goal that eventually cost Madrid the match, but he's hardly placed a foot wrong apart from that this season.
Central midfielder: Ivan Rakitic

This is a tough choice considering Luka Modric, Arthur Melo and Isco are some other options for this position, but Rakitic's fine form this season gives him the edge.
With all due respect to his compatriot Modric, the Croatian is now 33 years old and is nearing the end of an incredible career. Arthur and Isco are both immensely talented players, but they haven't had as much game time as Rakitic so far. He is still at the top of his game, and a crucial component of Barca's midfield.
One of Barcelona's highlights of this season has been his thunderous volley that he buried in the 4-2 win over Tottenham in the Champions League. Valverde could use something like that from him on Sunday.