The eyes of the whole world will be firmly set on Nou Camp this Sunday when Barcelona lock horns against Real Madrid to contest the 233rd edition of El Clasico and the importance of victory for both sides on the night cannot be stressed enough.Heading into the clash, Barcelona and Real Madrid are separated in the table by a solitary point and the victor on the night is eventually expected to go on and lift the prestigious La Liga title. While the reward of the win is certainly a huge one, the repercussions of defeat could prove to be very damaging as well – especially for the under pressure manager’s of the two teams. Therefore, the term ‘must-win’ seems perfectly apt for Sunday night’s El Clasico and here are the players who will be key in deciding the outcome of the game. Cristiano Ronaldo – Real Madrid Cristiano Ronaldo is a rather obvious choice but there is no denying that if Real Madrid are to come away from their trip to the Nou Camp with a victory, the Portuguese superstar will prove to be an integral figure. Ronaldo certainly loves the big occasion and this can be epitomized by the fact that the 30-year old boasts a wonderful record of 14 goals in only 22 El Clasicos. While it might sound strange for a man who has already scored 41 goals this season, Ronaldo has been enduring a roller coaster campaign so far. Following the highs at the start of the season, Ronaldo has received a lot of criticism in recent times and his sulking attitude has been made apparent by his refusal to speak to the media till the end of the season. Therefore, Ronaldo will be determined to shut his critics up with a good performance in the biggest stages of them all against Barcelona this weekend and he will surely need to perform to his best in order to help a stuttering Madrid side to victory against their perennial rivals. Lionel Messi – Barcelona Another obvious selection, Lionel Messi has been synonymous with El Clasico and the Argentinean star simply loves playing against Real Madrid. The all time leading goalscorer in El Clasico history, with an amazing 21 goals in 29 appearances, Messi usually has proven to be the difference for Barcelona against Madrid and one can be sure that the diminutive striker will be vital to the Catalans’ chances on Sunday. While Ronaldo’s campaign may have been a roller coaster one so far, Messi is enjoying a remarkable upward curve at the moment and heads into the game on Sunday as arguably the most in form player in Europe. Things are starting to click for Barcelona during a crucial stage of the season and if Messi can guide his side to all three points against Real Madrid on Sunday – the Catalans could well have one hand on the prestigious La Liga title. Luka Modric – Real Madrid There is no doubting that after Ronaldo, the most important player for Real Madrid is Luka Modric. While the duo of Karim Benzema and Gareth Bale might want to disagree, Modric is simply indispensible for Madrid’s plans and is the fulcrum around which Los Blancos base their entire game plan on. A midfield orchestrator of the highest order, Modric makes the Madrid symphony run smoothly and after Ronaldo – the Croatian international is surely the first name on the team sheet for manager Carlo Ancelotti. As a testament to Modric’s importance, Madrid look a much refined unit when they claimed a convincing 2-0 victory over Levante last time out and Modric will surely need to combine well with midfield general Toni Kroos this weekend in order to guide Madrid to a victory over Barcelona. Ivan Rakitic – Barcelona Many eyebrows were raised when Barcelona decided to offload Spanish star Cesc Fabregas to bring in the less flamboyant Ivan Rakitic over the summer but it has to be said that the Croatian’s signing has been justified. Rakitic has proven to be a vital member of the Barcelona squad and has fitted seamlessly into the star studded Catalan midfield. A player with pin point passing accuracy, Rakitic provides also the sort of defensive solidity that Fabregas did not and to shine in a midfield lineup consisting of the likes of Xavi, Andres Iniesta and Sergio Busquets, speaks volumes about his talent. Rakitic delivered a master class during Barcelona’s 1-0 victory over Manchester City in the Champions Legaue recently and he is undoubtedly, the Catalans’ answer to Luka Modric and it will be interesting to see who will come out on top in the battle of the Croatian maestros. Sergio Ramos – Real Madrid Defensive solidity and Real Madrid has not gone together in recent times and their woeful performance against Schalke in the Champions League typified this fact. Therefore, Madrid fans were left fearing the worst a few weeks ahead of the clash against Barcelona. As a huge boost for Madrid though, the return of Sergio Ramos has served to allay such fears and the Spaniard’s return could not have been better time. Ramos has been a pillar of strength in the Madrid backline over the years and his mere presence seems to transmit confidence to his fellow defenders. It goes without saying that Ramos will be crucial for Madrid against Barcelona and although it will be a tough task, the 28-year old is more than capable of stopping the dangerous trio of Lionel Messi, Luis Suarez and Neymar.