World number one Roger Federer believes local hero Lleyton Hewitt could be his biggest threat at the Australian Open. Federer, who starts as the overwhelming favourite to defend his crown over the coming fortnight, said he believed home-turf advantage would give in-form Hewitt an edge over the rest of the men's field "Because it's in Australia, I would have to pick Lleyton," said the Swiss star, when asked who his main rival would be.