Novak Djokovic warned his Wimbledon rivals on Sunday that he still hasn't reached his full potential as the world number one bids to move a step closer to a historic calendar Grand Slam.
Djokovic is a strong favourite to win Wimbledon for the fourth time after lifting the trophy at the All England Club for the last two years.
Beating Andy Murray in the French Open final earlier this month brought the Serb the only Grand Slam missing from his collection and if he can retain the Wimbledon and US Open titles he will become the first man since Rod Laver in 1969 to complete a remarkable sweep of the four major prizes in one year.
But, on the eve of his Wimbledon first-round tie against British wildcard James Ward, Djokovic made a revelation about the need to further improve his game that should give his fellow contenders for the title a few sleepless nights.
"Obviously I'm at the peak of my career at the moment. I see still lots of room for improvement, things that I can work on," Djokovic told reporters at Wimbledon.
"That's something that encourages me. That's something that keeps me grounded in a way, gives me more reason to practise.
"I can certainly say I've been working hard to get consistency on all kinds of surfaces."
While Djokovic might see a few imperfections that can be worked on, those flaws have been almost impossible for opponents to detect.
The 29-year-old has won six of the last eight Grand Slams, taking him to a career tally of 12 - within two of Rafael Nadal's mark and five behind the record 17 of Roger Federer.