Novak Djokovic
Djokovic will play at Aegon International for match practice on grass ahead of WimbledonReuters

Tennis ace Novak Djokovic conceded that he is not playing to the best of his abilities and that he has been experiencing the toughest phase of his career in the last "seven or eight months."

The Serb, who became the first man since Rod Laver in 1969 to hold all four Grand Slam titles last year, has fallen from the top-two spots of ATP rankings for the first time since 2011. The fourth-ranked tennis star has suffered a year-long title drought, with his ongoing season going from bad to worse.

The very fact that Djokovic is playing a tournament on grass -- Eastbourne International in Nottingham -- ahead of Wimbledon for the first time since 2011 shows how desperate he is to get back to his best before the season's third major tournament kicks off on July 3.

"I have been struggling with the level of tennis. I have never experienced this particular situation since I started playing professional tennis. I was very fortunate to experience upwards direction in terms of results and improving the game," Djokovic said on the eve of his Aegon International first-round match against Vasek Pospisil, BBC reported.

He added: "It is the first time now in a stretch of seven or eight months that I have not won any big tournament."

Djokovic was on a roll when he won the career Grand Slam after making his way to the top step of the podium in Roland Garros last year. However, a shock third-round exit in Wimbledon kickstarted his downfall. Despite battling with a wrist injury, the Serb made the final of US Open only to lose to eventual champion Stanislas Wawrinka.

After conceding the world number one tag to Andy Murray towards the end of last season, the 30-year-old also lost the final of ATP World Tour Finals to the Scot in straight sets.

It looked like Djokovic would be able to turn things around when he won the season-opening Qatar Open, beating Murray in the final of the tournament. However, a second-round exit at Australian Open came as a shock to tennis fraternity, who were treated to some top-quality action from Rafael Nadal and Roger Federer, who stepped up to reach the final in Melbourne.

While he ended the hard court season with only one title, Djokovic showed signs of improvement on the dirt by reaching the final stages of Madrid Masters and Rome Masters. However, he was not able to make good use of his form on clay at Roland Garros as the defending champion was dumped out in the quarter-final by in-form Dominic Thiem.

Novak Djokovic
Djokovic failed to defend his French Open title earlier this yearReuters

Hoping for some match practice in Nottingham ahead of Wimbledon, Djokovic stresses the importance of staying positive. It will be an uphill task for the three-time champion, but it will be interesting to see how he regroups and goes about his business at SW19.

"I am not playing at my best and I am aware of that. But I have got to stay positive about myself and my game. It had to happen sooner or later and I am really glad it did - it made me start asking myself certain questions," Djokovic added.

"I know that things change: I am 30, not 20 and I have to adjust to that. Things evolve each year and you have to adjust and get the best out of yourself," he opined.