It's the eve of Chelsea’s Europa League home tie against Sparta Prague and David Luiz is walking around Stamford Bridge bringing a smile to everyone’s face.

This is a common sight for anyone who has been following the Brazil international since he joined from Benfica in a deal worth £25million just over two years ago.

Luiz’s personality is infectious, so much so that he became an instant hit in the dressing room despite not being able to speak much English at first.

All the jokes and that crazy hairstyle have made it easy for some people, though, to get the wrong impression.

For behind the laughter and bubbly personality is a young man of fierce determination, who is desperate for Chelsea to succeed.

No one was more upset at the club’s failure to lift the FIFA Club World Cup in Japan two months ago as his tears on the pitch following their 1-0 defeat against Corinthians showed.

It was the first glimpse many football fans had to this side of his character but Luiz is keen to stress that when it comes to his football career, he definitely sees it as no laughing matter.

In an exclusive interview with Standard Sport, he said: “Yes, I am a happy person but I also have a responsibility. I know the club I represent and Chelsea want to win.

“At the FIFA Club World Cup it was my dream to lift the trophy and it didn’t happen. That was the first moment people saw me crying on the pitch but I have lost other games at Chelsea and cried then, too — it just may have been in the dressing room afterwards.

“I’m a joker, that’s my choice. It’s my style. But I care about my life, I care about the game, I care about the people who gave me this opportunity.

“Chelsea gave me the chance to play in the best League in the world, so I care about other things.

“I know what is important. When I go to the pitch I cannot laugh, I respect the other players. I try my best and put my passion inside the game.

“I like to have fun but there are moments you need to show yourself and that for me is on the pitch.”

Luiz’s resolve has earned the admiration of his team-mates and he is valued as a key figure in the dressing room.

Chelsea need new characters to emerge for veterans Frank Lampard, captain John Terry and Ashley Cole can’t play on forever.

It is a role that Luiz thrives in and he added: “This is my personality. Other players can be leaders on the pitch but not all players can understand another player, so I try to.

“You need to understand the heart of another player. I try to read other people, to figure out how I can joke with this guy, how I can help him or touch his heart.

“It makes me a leader but I have always been like this. I was captain of Benfica at 21 and they are a big club. I don’t do things just to look a good guy, I do it because I feel it. I am not fake. It’s coming from inside me.”

Brazil coach Luiz Felipe Scolari has noticed these qualities, too. He made him captain for the friendly against England earlier this month and is sure to select him in his squad again for the friendly against Russia at Stamford Bridge on March 25.

But it is his playing style that has also been commanding more respect over the past 12 months after inevitably taking time to adapt to the English game.

In recent weeks Luiz has impressed as a defensive midfielder, yet his performances at centre-half have also reached a high standard, as was shown during Chelsea’s remarkable surge toward the Champions League trophy last season.

Barcelona continue to cast admiring glances but significantly Luiz signed a new five-year contract in September to commit his future to the club.

Luiz is aware of his development in a blue shirt and added: “I have grown stronger. Now I am more mature.

“I know more about football in the Premier League, I know more about another country.

“I have developed a lot of things and this has made me strong.”

It is also why he will not be taking anything for granted when Chelsea play against Sparta at home in the Europa League tonight.

Chelsea boast a 1-0 lead from the first leg of their last-32 tie, yet Luiz is aware that a lack of focus was one of the reasons why the Blues were knocked out in the Champions League group stage before Christmas.

Some have questioned if the team are motivated to win Europe’s second-tier competition after the highs of Munich last May. But it is not a theory Luiz is keen to entertain.

“You need to be a champion every day, not just in one final,” he said. “Some people say last season you won the Champions League and now you only have this one.

“But last week I ate chicken and the next I day I had pizza. It’s different food but still tastes good.

“I am very hungry to win titles and to give people many more good feelings and great moments. For sure, if we win the Europa League this year, we will have the same celebrations as we had last year.”

“It’s important we take Sparta seriously from the start. If anyone doesn’t want to play this game, then they should stay at home.”

As can be seen, when it comes to his football, Luiz is certainly not fooling around.

‘ . . . and it’s intensity, not bullying’

DAVID LUIZ has defended his tackling style and insists he is not a dirty player.

Luiz was criticised for his heavy challenge on Jake Reeves last Sunday, when his shoulder collided with the Brentford player’s face (right) just before the end of Chelsea’s 4-0 victory.

Reeves had to be substituted and it prompted former Arsenal striker Ian Wright to accuse Luiz of being a ‘bully’. But the Brazil international, who visited the Brentford dressing room after the final whistle to apologise, is adamant it was an accident.

He said: “I didn’t try to hurt the guy. I was just trying to be strong and didn’t mean to go so high. I arrived a little late but it wasn’t intentional. I could show you 30 challenges that have been worse over the season.

“I play with intensity but I never want to hurt another player. I gave my shirt to him and told him I was sorry. I wanted to know if he was okay. He gave me a hug and I wished him good luck for the future.”

Watch Brazil play Russia on Monday March 25 at Stamford Bridge. Tickets are on sale at the stadium box office, by calling 0871 984 1905 or going to www.chelseafc.com/tickets. Prices start from £25 for adults and £12.50 for juniors /seniors.