I'm one injury away from hanging up the racket at any time.

I have sometimes played my best Davis Cup matches away from home when you stay in the moment a bit more. But it is tough when half the crowd are spitting on you.

Maybe if you're playing in London or America, you don't feel that pressure quite as much.

Why'd you leave the match, huh?

That's when you've got to grit your teeth and hang in there and try and find a way to win when you're not playing your best tennis - that's what I can be proud of

I feel like when I'm match tough and match hard and played a lot of matches I got that competitive winning spirit going and I can get on some rolls like I did last year. I won San Jose, Indian Wells and made the semifinals in Miami so it can happen for me.

I was lucky enough to win the Davis Cup in my first year in 1999. I won my first slam at the U.S. Open in 2001 and became world No. 1 later that year. By the age of 20, I'd done it all.