Novak Djokovic believes it is "pretty much an open field" at Wimbledon this year despite the fact that he is an overwhelming favourite to successfully defend his title.

Djokovic completed a calendar Grand Slam by claiming an elusive first French Open title at Roland Garros this month and the world number one currently holds all four major titles.

The 29-year-old Serb is halfway to becoming the first man since Rod Laver back in 1969 to pull off a calendar Grand Slam and has warned his rivals he still has room for improvement.

Djokovic is undoubtedly the dominant force in the men's game, but the top seed feels a number of players are capable of dethroning him at SW19.

He said: "You always have the top players, the ones that were most dominant on the grand slams in the previous years that are always in contention of winning the trophy.

"Andy Murray, Roger [Federer] first of all, because of their rankings, their history of playing, playing well, and winning this tournament, especially Roger so many times. 

"Then you have, I think, Milos Raonic, who has been playing very well. He has a big serve, which is an obvious advantage on this surface that is quickest we have in sports. 

"[Nick] Kyrgios is definitely one of the players that can go far. 

"I think it's pretty much an open field. But I think the beauty of all the grand slams and of this sport is that you always start from scratch and you always start from the same starting position as everybody else, fighting for the trophy equally as everybody else."

Djokovic starts the defence of his title against James Ward on Centre Court on Monday.