Boris Becker has pinpointed a change in mindset as the main reason for Novak Djokovic's recent struggles on the ATP tour. The Serb lost his number one ranking to Andy Murray at the end of last year and has struggled to get going this season.

Djokovic won the opening tournament of the season in Doha, when he beat Murray in the finals, but has since failed to go past the quarter-finals in any of the four events he has played. Becker believes the 12-time men's singles Grand Slam champion lost his edge after his win at the French Open last year, which put him in an illustrious group of eight players to have won all four major titles during their career.

The Serbian tennis star, who revealed earlier in the season that tennis was not his number one priority at the moment, has been backed to return to form sooner rather than later. However, he suffered his fourth straight loss before the semi-finals in Monte Carlo last week and Becker feels that other players are taking his lack of form as an incentive to get a big scalp.

"You cannot lose your forehand or your serve overnight, but I think it's his mindset. I think a lot has changed for him winning the Grand Slam last year at the French - it was his lifelong dream, and then you pop the balloon and the air went out and he hasn't got the air back," Becker said, as quoted by Tennis World USA.

"The locker room doesn't sleep. You see a weakness from a top guy and they want his scalp. They're reading his body language, and also getting smarter in how to play him so that's another problem. Once you've been dominating for so long and won so many times, eventually the tide will turn. He's still 29 so he has time to re-arrange the ship and get in the right direction, but he has to do it soon."

Roger Federer, meanwhile, has been labeled an 'all time great' by the German after the Swiss ace came back from a six-month injury absence to win three of the four tournaments he has played in 2017. The 35-year-old won the Australian Open to make it 18-Grand Slam titles and followed it up with the sunshine double at the Masters Series events in Indian Wells and Miami.

"He started the year by winning Australian Open, Miami and Indian Wells, but we should not be surprised because he is the all time great and one of the greatest sportsmen ever," Becker added.