Coentrao will be out almost a month. But he will recover soon enough to start in Real Madrid's leftback while Marcelo recovers from his ankle injury. Marcelo isn't expected to come back before the end of 2012, and he could even need more time than that to get in shape, since it's very important to be physically ready to play in that position.
Luckily enough for Real Madrid, Jose Mourinho signed Fábio Coentrao from Benfica in the summer of 2011. Marcelo is the world's greatest leftback, so not many people understood Real Madrid's 30M€ move (20M€ if you consider Garay's departure from the club). But Coentrao has been useful against Barcelona for example. Now, his time has come. Coentrao will have almost two months to prove himself.
The Portuguese leftback is a very capable defender. He was selected as the best leftback in South Africa's FIFA World Cup. He's also a valuable asset in Real Madrid's offensive plan, although he's not as good as Marcelo. The afro genious tends to move from the left wing to the center of the pitch, while Coentrao is more vertical and goes for the cross a lot more often. That would allow Cristiano Ronaldo to use his brilliant aerial game.
In Real Madrid's next few games until Coentrao recovers, Mourinho will probably play Álvaro Arbeloa in the left wing, just in the same position he performed a lot under Manuel Pellegrini. If that's Mourinho's choice, Essien or Sergio Ramos will need to play as right backs. It'd probably be better to let Ramos play there and put Varane or Albiol alongside Pepe, but Mourinho clearly trusts Michael Essien, even though he's not fit enough to play as a fullback yet.
One way or another, Real Madrid's trip to Dortmund next week will be a tough fixture. And there still are some International games to play this Tuesday. Mourinho can't afford to lose any more men in this FIFA break.