Rafael Nadal has admitted that he is still struggling with knee issues following a serious injury last year.
The Spaniard, who returned to action in February following a lengthy stint on the sidelines, has since regained the world number one spot from Novak Djokovic.
Despite an impressive season, the Spaniard has admitted that he still experiences trouble with his knee.
"It's true that when the bounces are lower for me, today it's a little bit tougher," Nadal told BBC Sport. "The knee is not 100% but it's not the moment to think about that."
Nadal will begin his campaign at the ATP World Tour Finals in London by taking on David Ferrer this afternoon.
