Real Madrid v Barcelona: The key questions in Sunday's pivotal El Clasico

Zinedine Zidane, Karim Benzema, Lionel Messi and Martin Braithwaite are all talking points going into El Clasico

With 13 games remaining and Barcelona leading Real Madrid by two points, El Clasico at the Bernabeu on Sunday could be pivotal in deciding the most compelling La Liga title race for years.

Neither team has looked particularly convincing this season, both have been hit by significant injury blows, and Real now have a Champions League home defeat to bounce back from, so there are plenty of uncertainties heading into a game that is likely to be tense and closely contested.

Here are some of the key storylines to look out for on Sunday.

Can Benzema carry the load for shot-shy Real?

A notable aspect of Real's season has been their struggle in front of goal, which came to light once again during last weekend's shock 1-0 loss at mid-table Levante - the eighth time this season they have failed to score.

During the early phases of the campaign, Karim Benzema carried the load almost single-handedly. The Frenchman netted 13 goals in the first 16 league games, masking the team's overall deficiencies inside the penalty area.

But Benzema has mustered only one league goal since Christmas - an important one, winning last month's local derby against Atletico Madrid - and none of the team's other forwards have stepped up to play their part.

A remarkable stat this late into the season is that excluding penalties no other Real player has scored more than three league goals. Sergio Ramos is the team's second-highest scorer with five, but three of those came from the spot.

The team's forwards are, to be blunt, having very bad seasons in front of goal: Gareth Bale (two league goals), Eden Hazard (1), Luka Jovic (2), Rodrygo (2) and Vinicius Junior (1) have all massively underperformed, making the ability of midfielders like Toni Kroos and Fede Valverde (and, of course, Ramos) to chip in with their fair share of strikes extremely important.

To an extent, injuries can be blamed for the forwards' lack of goals, and last weekend's loss at Levante provided another major setback as Hazard - in just his second game since returning from a three-month absence - limped off with a fractured ankle that is likely to keep him out for the rest of the season.

In stark contrast to the Real team of Zidane's previous managerial stint, which often struggled to play cohesive football but never lacked goalscoring prowess - largely thanks to Cristiano Ronaldo - the current side are more than capable of knitting together pretty passing patterns but regularly fail to be effective where it matters the most.

Barca's injuries at the back, options up front

Could Martin Braithwaite, who ended the transfer window with Leganes, play in El Clasico?

Barcelona will be missing their first choice full-backs, with Sergi Roberto and Jordi Alba injured. They will be replaced by the uninspiring duo of Nelson Semedo and Junior Firpo, and there is also a doubt over Gerard Pique after he hurt his ankle during Tuesday's draw at Napoli.

Further forward, recently installed manager Quique Setien has plenty of options to support key man Lionel Messi, who has again carried the team this season by recording league-high totals of 18 goals and 12 assists.

Against Napoli in midweek, Setien opted for Messi and Antoine Griezmann in attack, stacking the midfield with a narrow quartet of Sergio Busquets, Ivan Rakitic, Frenkie de Jong and Arturo Vidal.

He may opt for a similar selection this weekend, but a pair of intriguing options are available. Firstly, teen star Ansu Fati offers width, goalscoring and a welcome dose of the unpredictable, and his inclusion would add another dimension to the team's otherwise undermanned attack.

The real wildcard, however, could be former Middlesbrough misfit Martin Braithwaite, who became a surprise emergency signing last week after Ousmane Dembele was sidelined for six months.

Braithwaite made a promising debut off the bench against Alaves last weekend, assisting the last two goals. The Danish striker still has to prove that he can make a meaningful contribution at moments that matter, but he does offer the pace and directness which are otherwise lacking.

Maintaining control or risking penetration?

The top of La Liga before any of this weekend's games

December's meeting was the first goalless draw between the teams since 2002, and this weekend's showdown could well be a similarly cagey affair.

With just two points between them at the top of the table, the stakes are high - especially as head-to-head records, not goal difference, separate teams level on points in La Liga. That means Sunday's game is effectively worth an extra point to the winner, so avoiding defeat will perhaps be more tempting than chasing victory.

A key tactical question will be whether managers Zidane and Setien pursue cautious control or take risks to find penalty box penetration.

In the same way that the Barca boss must choose how to complement Messi and Griezmann, Zidane's dilemma is how he can build his team's attacking play around Benzema.

Bale should be the obvious option, especially with Hazard out, but the Welshman has done little in recent weeks to justify starting. Wingers Vinicius and Lucas Vazquez could also be used, but Rodrygo is unavailable through suspension after getting sent off with the club's B team last weekend.

Zidane, who loves varying his team selections and springing surprises, could also follow Setien's method and overload his midfield, with Casemiro, Kroos, Valverde, Isco and Luka Modric all doing more in recent weeks to earn a starting spot than any of the forwards.

Setien, meanwhile, is an avid adherent of possession football: his team attempted more than 1,000 passes in a home win over Granada, while his insistence on building from the back led to goalkeeper Marc-Andre ter Stegen making 69 passes earlier this month against Getafe.

So Barca could well dominate possession, but can they use it to provide Messi and Griezmann with ammunition?

This Clasico comes with many unknowns. The answers could go a long way towards deciding this season's champions.