Former Russian tennis player Marat Safin believes something is "wrong" with the game if Rafa Nadal and Roger Federer are still heavily dominant forces.
Safin, 37, retired eight years ago after the 2009 Rolex Paris Masters.
The Russian is a former world No. 1 and a two-time Grand Slam and Davis Cup champion.
Nothing hasn't particularly changed since as Nadal, Federer, Novak Djokovic, and Andy Murray are still viewed as the superstars of tennis.
The 'Big Four' claimed most of the Grand Slam and Masters 1000 titles in the last decade or so.
Nadal, 31, is ranked at No. 1 in the world, while 36-year-old Federer follows him closely at No. 2.
Djokovic and Murray, who haven't played since Wimbledon, have dropped outside the top-10 as they're recovering from their respective injuries.
Rising world No. 4 Alexander Zverev is strongly bidding to become the next big thing after a strong 2017 campaign.
The 20-year-old won it all at Masters 1000 events in Rome and Montreal and reached a career-high of No. 3.
Dimitrov, 26, had a breakthrough season as well after winning his maiden Masters 1000 title in Cincinnati and making it all the way at the Nitto ATP Finals to reach his current career-high ranking of No. 3.
"If Federer and Nadal are still winning I think there's something wrong," Safin told The Independent. "I don’t see any upcoming superstars today.
"I'm not saying that our times were the best, but when I was growing up, players were winning ATP tournaments at 16, 17, 18. Now players are only just starting to be pros at the age of 25. I don't know why that is.
"Players used to retire by the time they got to 30. At 32 you were a dinosaur. Now you see players who are still running at the age of 38. The upcoming young guys just aren't at a high enough level. If you can still manage to run at the age of 38 and still be No. 1 in the world, it means there must be something wrong with the other players."
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