With Real Madrid and Barcelona set to meet in El Clasico on Sky Sports on Saturday evening, Guillem Balague previews the match, looks at the key factors and considers how significant the outcome will be in the title race...

Injuries and selection dilemmas

Messi has been training with the group since Thursday, which means he is available and should travel. Nobody expects otherwise. The problem is that he has been out for 54 days and Barcelona have done well in his absence with seven victories, one draw and one defeat. My guess would be that he starts on the bench - why risk him?

This is not a title decider and Messi has matured enough to realise the long-term benefits of coming back slowly from injury. Elsewhere for Barcelona, Rafinha is out for most of the season and Ivan Rakitic is doubtful.

For Real Madrid, the good news is that Bale and Ronaldo have not been away with their national sides and nor has Sergio Ramos, who has a painful shoulder injury. He gets painkillers before games and that limits him a bit, but he will play. 

Karim Benzema is the only doubt. He trained very well in the week but he has been out for longer than expected and it would be a bit risky to play him, so he might be on the bench, which is a serious problem for Real as he is crucial in attack.

Benitez has to decide if he plays Isco and also James, who has played with the national side but is maybe not 100 per cent. I think Real Madrid will play 4-4-2 with Bale and Cristiano up front and Isco, Kroos, Casemiro and Modric in midfield.

Formation and tactics

Without Messi, Barca have tried different formations - 4-2-3-1 and 4-4-2 - and I think they will, depending what happens with Rakitic, still have three forwards. That would mean Munir El Haddadi could play up front with Suarez and Neymar. When he has played he has worked hard and that's what Luis Enrique is asking for from him.

Mascherano is back so he will partner Pique in defence and Busquets, who has been fantastic, will be in front of them, with Claudio Bravo in goal.

Real Madrid need to find a balance between forwards that don't defend too much and a midfield that gets over-exposed if that happens. Benzema is not 100 per cent and he is absolutely crucial to gel the players up front - to make Ronaldo and Bale better with the one-twos and runs to create space. If he does not start that means adding another midfielder which could make life difficult for Barcelona. 

The line of pressure will be key. If Benitez feels that Real Madrid have got the physical strength they will pressure high for a few seconds to make life tough in the build-up for Barcelona.