Arsene Wenger believes Barcelona are the best team in the world but manager Pep Guardiola says his players could be "chasing shadows" if they are not at their best against Arsenal tomorrow night.
The Catalan giants are favourites to win the UEFA Champions League, and Wenger was quick to concede his side would be underdogs against a team he says are setting the standard in club football. Barça won a two-legged quarter-final against Arsenal in last season's competition, drawing 2-2 at the Emirates Stadium before administering a 4-1 thrashing at the Nou Camp.
Guardiola has promised to remain true to the Barcelona way in tomorrow night's last-16 clash, with possession and attack the order of the day, though he admits Wenger's style of play could leave his side on the back foot if they are not in top form.

"With Arsenal, if you are not well prepared you will be chasing shadows," said Guardiola. "I like to watch Arsenal play football but I don't like to play against them. Of course I have worries about the game that Arsene Wenger plays. Theo Walcott has some good moments, Wenger is an incredible coach and Robin van Persie is a very mobile player who has a lot of influence.
"When you play Arsenal you know what is required of you. The players of Barcelona know what we have to do. We will try to play attractive football, we have for the last 20-25 years. We might lose, we might win but we will always play attractive football for our fans."
Guardiola, whose side drew against Sporting Gijon last weekend, has pinpointed at least one away goal as the minimum requirement for the first leg and is sure there will be little to pick between the sides going into the return fixture.
"The main objective is to play well, to try and dominate all the play," he said. "We will try and score a goal because scoring away from home is very important. We want to bring at least a goal back to Barcelona. But I don't think it will be decided tomorrow. We will have to decide it in Barça in the second leg."
Arsenal playmaker Samir Nasri, the Gunners' 14-goal top scorer, could feature tomorrow as Wenger ponders whether to rush him back after a fortnight out with a hamstring injury. 
Despite his threat, Guardiola admires the Frenchman and wants him play. "If Nasri doesn't play they still have (Tomas) Rosicky or (Andrey) Arshavin but Nasri is an incredible player. I hope Nasri can play. I always prefer to play the teams who have the best players."