London risks losing ATP Finals: Nadal

The Spaniard believes the 50 percent tax on players' appearance fees, winnings and a proportion of their worldwide endorsement earnings could see the glamour event featuring the top eight men being staged elsewhere unless the law is changed.

"It is really tough what is happening today in the UK with the tax. There are a lot of things that are really positive. This (tax) thing is probably really negative," he said after losing in the third round to German Florian Mayer.

"What I believe in my heart, is that London is a fantastic event. There's a full crowd at every match, a fantastic stadium. But London is not the only city in the world," he said.

The five-year contract for the ATP World Tour Finals, staged at the 02 Arena, comes up for renewal in 2013 but Nadal indicated that growing discontent could see players pushing for the event to be moved to a more favourable tax environment.

"The tax regime from UK is complicating a lot of things because to go and play at Queen's, the problem is not to win. The problem is I can lose money because I go there. I play for one week, and they take out money from my sponsors. That's a lot," he said of the Wimbledon warm-up event.