Barcelona are hot favourites to become the first team to defend the European Cup in the Champions League era and are currently on a 32-game unbeaten run in all competitions. Cheap Yeezy 350 . So how can Arsenal stop them on Tuesday night? Start with Sergio Busquets… Unstoppable. Thats the verdict of many regarding this Barcelona team. There might be 16 clubs left in this seasons Champions League but the current holders are little more than 2/1 to retain the trophy in May. Its a side full of players capable of hurting the opposition.Luis Suarez is the top scorer in Spain, while Lionel Messi recently reclaimed the Ballon dOr for a record fifth time by edging out fellow Barcelona forward Neymar. But if all that sounds so daunting that Arsenal need not show up on Tuesday, there might be hope nevertheless. Even the most beautiful of machines requires an engine and Barcelonas is Sergio Busquets. He is a fundamental player for us, said coach Luis Enrique earlier this season. When he is there the team gains solidity in defence and attack. He is a unique player. Busquets has been described as fundamental by coach Luis Enrique Fundamental. Unique. And worth stopping. Barcelona might be unbeaten in 32 games but there is some evidence that disrupting Busquets can have an impact on the teams fluency. Thats something opposition sides appear to have picked up on this season.Some teams are opting to press Barca. It means being brave and abandoning the tried and trusted method of stifling Barcelona - a template made famous by Jose Mourinhos Inter side in 2010. But its a tactic that Arsenal might well be better suited to employing.We saw team after team play a narrow back-four, tuck their wide midfielders into a back-six and completely give up on possession, explains Sky Sports Spanish football expert Terry Gibson. You tracked runners and plugged gaps and hoped to somehow stay in the game. I think a lot of teams recognise now that if you stop, surprisingly enough, Sergio Busquets, and put him under pressure it forces Barcelona into going a little bit more direct than they would like. Terry Gibson I believe now that more teams are pressing them high up the pitch. I think a lot of teams recognise now that if you stop, surprisingly enough, Sergio Busquets, and put him under pressure it forces Barcelona into going a little bit more direct than they would like.They can go direct, but its normally balls played into channels, slid down the side for Suarez, rather than the long clearance from Javier Mascherano thats easy for a centre-half to clear. Its the latter that you want to try to force Barcelona to do.Pep Guardiola attempted this uber-aggressive approach with Bayern Munich in the Champions League semi-final first leg last season. The tactic was dismissed by some as reckless. But as so often with Guardiola, he might just have been on to something. Eduardo Berizzo, a fellow Marcelo Bielsa admirer, enjoyed spectacular success in coaching Celta Vigo to a 4-1 win over Barcelona in Galicia in September. Playing a high-pressing game, they were all over the visitors, leaving Barcelona - and Busquets, in particular - rattled.Roberto Rodriguez, writing in Catalan newspaper La Vanguardia, reported that Celta raised a cyclone of total football and that the team suffered, especially Busquets who was said to be overwhelmed and found little support