With Gonzalo Higuain out injured for four months, Real Madrid have a heavy reliance on 22-top goal scorer Cristiano Ronaldo.
Real Madrid need a striker to topple Barcelona
Barcelona are Spain's winter champions. The Catalans lead the Primera Liga table at the halfway point, having played every team once.
In their 19 games so far, Pep Guardiola's side have won 17, drawn one and lost one.
Never before have they accumulated so many points at this stage in the season and with 61 goals scored, they have netted an average of 3.2 goals per game - over a goal per game more than Manchester United, the leaders of the English Premier League.
Barca are the first team since Real Madrid in 1961 to score 60 goals by the halfway stage. They have gone on to win the league eight of the nine times they were winter champions - the exception being 2006/07 when they were narrowly beaten to the title by Real.
Despite losing 5-0 to Barca earlier in the season, Real are again their main challengers. The Catalans' position was strengthened at the weekend, not only by their 4-1 victory over Malaga on Sunday, but by Real's unexpected 1-1 draw away at Almeria.
Jose Mourinho's side dropped two valuable points against a side which Barca beat 8-0, but the Portuguese manager claims that the league "is still anybody's".
"The draw is two points lost," he said, "but there is still the whole of the second half of the season to be played. And we hope to improve in the second half of the season."
Real may be four points behind Barca, but as Mourinho pointed out: "We have done well so far. We have won 15 matches, lost one and drawn three, but it isn't enough to be champions."
Real's form is impressive for a team coming together under a new coach, but their need for a goalscoring centre-forward to replace Gonzalo Higuain, the injured Argentine who is out for another four months, has become acute ahead of the resumption of the Champions League.
Cristiano Ronaldo, their 22-goal top scorer, may be Spain's leading marksman, but without Higuain they lack other options.
Mesut Ozil and Angel Di Maria, their next highest scorers, have netted just five times so far this season.
In contrast, Barca already have three players in double figures - Pedro, David Villa and Lionel Messi.
Real are trying to get Ruud van Nistelrooy, their former striker, back to the Bernabeu on a six-month loan deal.
The Dutch forward, 34, was Real's top scorer when they last won the league in 2007 and 2008, but his current club Hamburg are reluctant to let him go.
Real's second target is Carlos Tevez and while the Manchester City striker may like the appeal of playing in the Bernabeu, he has been more settled at Eastlands recently and his club would not entertain the idea of selling him.
Real's striker issue is causing problems at the club, with Jorge Valdano, the director general, suggesting that Mourinho made an error by leaving Karim Benzema on the bench against Almeria.
The Frenchman has started 11 of Real's 19 games from the bench and has scored just once in his last six starts.
"Ultimately, we are spectators to whatever the coach wants to do," said Valdano, before adding that Benzema was "a good striker who can give us many options going forward. I hope Benzema does not stay on the bench for too long. The situation surrounding him is unfair."
Such conflicting opinions aired publicly would be unthinkable at Barca, where Guardiola's authority goes unchallenged.
Real have always been a different beast, but discord does not help when they are setting out to do the impossible - trying to surpass the best team in the world.