Spanish playmaker looking forward to Champions League semi-final with the Catalan giants, but admits his side will be underdogs going into the last four of the competition.Juan Mata has warned that Chelsea will have to contend with more than just star player Lionel Messi when they meet Barcelona in their Champions League semi-final clash.The Argentine attacker has scored more than 50 goals this season and is widely acknowledged as the best player in the world at the moment - if not all-time.But Mata believes the rest of the Barcelona team are also more than capable of causing trouble for their opponents.\"Barca are a great side and all players can unbalance a match, it is not just Messi,” Mata told AS.Barcelona have won just once at Stamford Bridge in their five meetings in the Champions League, which will give the English side hope of overturning the reigning Spanish and European champions.Mata came through the Real Madrid youth set-up before forging a fine reputation at Valencia and admits Chelsea will be underdogs when taking on Pep Guardiola’s impressive side.\"They have not had an easy time at Stamford Bridge in the past, and let\'s hope that the same thing will happen now,2 he said\"We will see at the end of the season if we can say that this season was good. We have to play the semi-finals, but I have always said that Madrid and Barca are favourites to go through and be in the final.”Chelsea will welcome Barcelona to Stamford Bridge in the first-leg on 18 April before making the trip to the Camp Nou on the 24 April for the return leg.