Tonight Michael Ballack will be back doing what he knows best. There in the heart of Chelsea's midfield at the Emirates will be the imposing figure of Germany's captain, bringing his they-shall-not-pass presence to a side not lacking in strong characters. It is where Ballack wants to be, and right now, it is where he has never been more grateful to be.

Two Sundays ago, Ballack walked out in front of thousands of fans in another stadium, Hannover's AWD Arena - but not for a game. In his hands, instead of a ball, Ballack clutched a wreath, which he placed in the centre circle in front of the coffin of Robert Enke, the German goalkeeper who committed suicide.

"I knew Robert since he was 13 because we played each other in East Germany, when he played for Carl Zeiss Jena," says Ballack. "He was one of the players I had known for such a very long time. It was terrible for all the players. You lose a friend."

The two players were team-mates for the national side and would have taken the field together in next summer's World Cup finals in South Africa, but no one, neither team-mates nor family, was aware of the extent of Enke's enveloping struggle with depression.

Enke's team-mates had been there to support him in 2006, when his young daughter Lara died from a rare heart defect. What they did not realise however was that Enke continued to suffer from depression long afterwards, so much so that he was afraid that Leila, the daughter whom he and his wife Teresa adopted in May this year, might be taken from him if his anguish was ever made public.

Ballack pauses before speaking. "We never had the feeling that he had a problem like this," he says. "To not know that he has depression - that makes you feel helpless because you can't change it. This is a bad, bad thing. On Tuesday evening when we got the message in the team hotel, it was a shock. There was quietness and a lot of tears.

"I think we have to learn from this. There is the illness but also the combination with football and being famous. He was scared to speak about his problem because he was scared to lose his child, or his job. Or to confess to having a weakness to other players. People have weaknesses, we should accept it."

The relentless nature of football means that Ballack has little time to reflect on his grief for his lost friend, but must get back to playing. Tonight's trip to Arsenal is ripe with significance. Since moving to Chelsea in May 2006 on a free transfer from Bayern Munich, Ballack has won two FA Cups and a Carling Cup. Not bad, but perhaps not quite what was expected at the time as Chelsea, under the managerial guidance of Jose Mourinho, had just completed back-to-back titles.

The German freely admits he came to Chelsea to win the Champions League, an ambition yet to be realised by both player and club, but acknowledges that Manchester United have been the better side for the past three years.

"I knew what to expect," he says. "To come to a great, experienced team, I did not expect it goes like this, easy, to win the league every year. The other teams are too strong for this. I came here to win trophies. To win the Champions League, that's why I came here. There is still a big chance with Chelsea, with this team.