Novak Djokovic's loss of form, Andy Murray's loss of confidence, Rafael Nadal not being fully fit and Roger Federer's surprise form have all left the ATP Tour "very open" this year according to world number 38 Feliciano Lopez.

Murray and Djokovic ended last season as the world's number one and two respectively and continue to maintain their places at the top, while Nadal and Federer had to cut their 2016 season short due to injury. The Swiss ace stopped playing in July while the Spaniard ended his season in October.

The Serbian won the first tournament he played in 2017 beating the Scot at the Doha Open, but since then both the players have struggled for form and fitness. Djokovic has not progressed past the quarter-finals in the past four tournaments he has played, while Murray has similarly struggled to reach the latter stages.

Nadal and Federer, meanwhile, are the two best players this season having made five and three finals respectively. The former lost the first three finals he played — two against Federer and one against Sam Querrey — but won the next two in Monte Carlo and Barcelona. The latter made three finals in the four tournaments he has played thus far winning at the Australian Open, Miami and Indian Wells.

"Yes it is. Djokovic is not like he was, Murray lost confidence since he got injured, Nadal is recovering, the only one who surprises is Federer. This year the Tour is very open," Lopez said referring to the unexpected start the top players have made to 2017, as quoted by Tennis World USA.

Federer's blistering form has been the biggest surprise of 2017 with the Swiss ace currently on a 19-1 win-loss run in the four tournaments he has played. His only defeat came at the second round of the Dubai Tennis Championships at the hands of unknown Evgeny Donskoy.

Lopez, however, admits that he had no doubt that the 35-year-old could return to his best despite missing six months with a knee injury. Federer has made it clear that remaining fit and peaking at major tournaments is his main goal in 2017 and he has reduced the number of tournaments he plays.

"Honestly I didn't have any doubt that after not competing for a such long time he could play at a good level because he didn't forget how to play.

"Also, he is very smart with the way he handles himself physically, with the way he prepares, in the small changes in his game and racket. Apart the talent he has, without any doubt the best one in the history, he handles very well his career. He used in a very good way the six months where he did not play. He was at a similar level of when he was world no. 1," the Spaniard added.