Abu Dhabi: Rising Australian star Nick Kyrgios, who shot to prominence with his shock win over Rafael Nadal in the fourth round of Wimbledon 2014, can win a grand slam but lacks the mental toughness to be the best player on the planet.

That’s the view of Kyrgios’ compatriot, Pat Cash, the 1987 Wimbledon champion, who is delighted with the emergence of the 20-year-old and his fellow countryman Bernard Tomic.

Cash also believes the prodigious pair – Kyrgios is in 30th place in the world rankings and Tomic, 23, is 18th – will thrive under the guidance of Australia’s new Davis Cup captain, Lleyton Hewitt, who won two grand slams in his illustrious career.

“I think Nick’s got the talent and he’s as good a young player that’s out there,” said Cash, speaking to media in his role as tournament ambassador at this weekend’s Mubadala World Tennis Championship in Abu Dhabi.

“The thing with being number one, as you can see from [Novak] Djokovic, is that you need to be consistent every week. Nick’s quite an emotional kid and he’s a little bit up and down. I think that might be the harder thing to do, to be number one.

“I think Nick can win a grand slam. If I was his coach, that would be the thing that I’d be aiming for.”

Of Tomic’s credentials, Cash added: “Bernard’s a very good player and very smart, but he’s got a lot of improvement to do physically. But both him and Nick have the perfect person in Lleyton to teach them lessons as he was one of the greatest competitors ever seen in tennis.”