London, June 23 (IANS): Six-time Major winner Boris Becker on Tuesday feared that tennis could be lacking big personalities and its popularity might sink in the near future if Roger Federer and Rafael Nadal call time on their careers.

The former world No.1 said the modern generation of male players have strengthened the image of tennis and there is huge expectation surrounding the upcoming Wimbledon tournament, with world No.1 Novak Djokovic, Federer, Andy Murray and Nadal targeting the title.

The quartet have 41 Major titles among themselves. Swiss maestro Federer (17), Spaniard Nadal (14), Serb Djokovic (8) and Scottish Murray (2) have dominated the sport in the last decade.

"I think the men's side is in a very healthy state, we have an increase in popularity from over 10 years ago and the numbers are staggering," Becker was quoted as saying by skysports.com.

"But the question has to be asked: what if Roger decides to quit or Rafa is not coming back? It's impossible to carry on with only Novak and Andy," he said.

Becker, who coaches Djokovic, has raised concerns about the shortage of consistent challengers outside the top four.

"You have a young group of Australians -- Nick Kyrgios, Thanasi Kokkinakis, who have good personalities and are interesting to watch, but there's a gap in between of players you don't know anything about. In two or three years' time, we have to be careful," he said.

Earlier this month, Murray issued an apology after microphones picked up bad language during his third-round win over Kyrgios at the French Open.

Becker believes the current stars of the ATP tour could be forced to repress their personalities due to the intense media scrutiny.

"Nowadays everything is so supervised and so observed and everybody is very judgemental," said the 47-year-old, who was nicknamed 'Boom Boom Boris'.

"We live in a day and age where players have to be guarded a lot, in who they are as people.

"There are microphones on the court and social media so there are a lot of occasions when players have to guard their emotions and that's unfortunate because you want to see the real person."

This year's Wimbledon winner is expected to come from the top four in the world and Becker, a three-time title holder, is predicting an enthralling fortnight.

"I think there's a very strong rivalry between Djokovic and Federer and between Djokovic and Murray and between Djokovic and Nadal," Becker said.

"These are the matches that everyone is looking forward to. Those are the rivalries that make the sport that everyone is fascinated by.

"For a long time it was Roger and Rafa, even though Rafa won most of the matches, but last year we had a couple of really good matches between Andy and Novak and I think those are the matches which make the sport special," Becker concluded.