"Based on physical ability Nick Kyrgios is the only guy that can even compare to the Big 3, but I still don't know, is it gonna explode? Is it just a time bomb?" - Andy Roddick

Andy Roddick believes Nick Kyrgios is at par with the Big 3 on physical ability but warned that the Aussie's body is unreliable in sustaining itself for several matches.

Kyrgios stunned World No. 1 Daniil Medvedev in the second round of the Canadian Open on Wednesday, winning 6-7(1), 6-4, 6-2. With this win, the Aussie has won 13 out of his last 15 singles matches on tour.

The two matches the mercurial Aussie did not win include his Wimbledon defeat against Novak Djokovic and the walkover he received from Rafael Nadal at the All England Club.

Nick Kyrgios will next face countryman Alex de Minaur in the Round of 16 in Montreal. Speaking about that match on Tennis Channel, Andy Roddick highlighted how the Wimbledon runner-up is currently enjoying the form of his life.

"Listen, if we're just going on balls and strikes here, Kyrgios is playing at a completely other level," Roddick said. "He has options, right. We are talking about is he gonna come in non-stop, is he gonna stay back."

The former World No. 1 believes Kyrgios has the tools to down De Minaur and heaped special praise on the 27-year-old's physicality. That said, Roddick pointed out that Kyrgios' body can collapse at any minute, given he is not used to playing this many matches in a row.

"So whatever De Minaur does, I think Kyrgios is able to adjust - he has that amount of variety I think," he said. "Just based on physical ability I think he's the only guy that can even compare to the Big 3 of this generation but I still don't know is it gonna explode - he's played a lot of tennis. Is it just a time bomb?"

The American believes Kyrgios is the favorite going into his match against De Minaur.

"Aussie on Aussie, sometimes it's weird when you play your friends. I don't know but I have a hard time betting against Nick Kyrgios right now," Roddick said. "I actually have faith in him staying the course for the first time ever."

"Nick Kyrgios has all the momentum coming in, but I think that De Minaur might sneak this" - Mark Petchey

Former player Mark Petchey also weighed in on the upcoming clash between Nick Kyrgios and Alex de Minaur on Tennis Channel.

The Brit expressed his amazement at the fact that the two Aussies have never faced each other on tour before.

"That's incredible isn't it? I'm amazed that it's the first time - I was checking the stats obviously when we looked in and I'm gonna be fascinated to see just in terms of strategically how they both play," Petchey said.

Petchey believes De Minaur's tactic of staying on the baseline on return will give him the edge against Kyrgios, as the latter could struggle to generate the angles on his massive delivery.

"Alex loves to hug the baseline on the return, he doesn't give you the kind of width, it's a totally different serving match really for Nick in terms of Medvedev so deep (and), Alex hugging and cheating in," Petchey added. "I quite like Alex's chances. Kyrgios has all the momentum coming in but I think that De Minaur might sneak this."