Barcelona will travel without Xavi Hernández. Xabi Alonso seems to be in the same situation. Real Madrid's key midfielder is still recovering from his pubalgia and needs some rest before the battle at the Old Trafford. That way, Modric will probably have the chance to start.
Real Madrid has a deep bench, so Mourinho could also put Carvalho, Albiol, Essien, Callejón, Morata and Kaká on the field. To save Ramos, Varane, Khedira, Ronaldo, Özil and Di María from last-minute injuries seems quite necessary, but it's hard to foresee Ronaldo missing a Clásico.
FC Barcelona should try to have their own revenge at the Bernabéu, but Real Madrid's fans shouldn't forget that los blancos won the important game. Yes, La Liga is a bigger trophy, but three points more make no difference when you have that big of a deficit already.
It'll be interesting to see how Mourinho plays his cards. The Old Trafford awaits.