Marin Cilic is "incredibly dangerous" and is capable of shocking Rafael Nadal at the Australian Open, according to Mark Philippoussis.
Nadal is the favourite to reach the semi-finals as he prepares to face Cilic on Rod Laver Arena on Tuesday.
The Spanish 16-time grand slam champion holds a 5-1 head-to-head record over Croatian sixth seed Cilic.
But Philippoussis, a two-time major runner-up, feels Cilic could stun Nadal in Melbourne.
"Obviously you've got Roger [Federer] and Nadal, but then you've got Cilic, who's an incredibly dangerous player," he told Omnisport.
"He's getting stronger and better with each match he's played and he has the game to beat Nadal.
"It's going to be a very interesting match."
Nadal has won the past five matches against Cilic, who last beat the left-hander in Beijing in 2009.
It's 7am and time to sip a and digest the Day 9 schedule on @RodLaverArena.-- #AusOpen (@AustralianOpen) January 22, 2018
Day: B. Bryan/M. Bryan v M. Matkowski/A. Qureshi; E. Mertens v E. Svitolina; G. Dimitrov v K. Edmund
Night: R. Nadal v M. Cilic; C. Suarez Navarro v C. @CaroWozniacki#AusOpenpic.twitter.com/YDFXLP8A3u