Juan Carlos Ferrero, who is coaching Alexander Zverev, says there will be tighter competition between the veterans and newcomers at the top of the men's game.
"I think it is going to get really competitive among the Big Four and the young players in the Top 10 who want to settle down in the top of the rankings," he told the *International Business Times*.
And Zverev is among those young players, having won two Masters titles this season and reached No. 3 in the rankings.
"They now begin to see him as a potential number one. Because he is able to make it," said Ferrero, adding that he is now concentrating on developing Zverev's mental toughness. "We are working a lot on that side of him, so far Zverev has not had to face this aspect of the game."
But No. 1 Rafael Nadal and No. 2 Roger Federer are still formidable, said the former Grand Slam champ. Nadal won his 10th French Open this season and also the US Open, his first Grand Slam victories since 2014.