But coaches and Davis Cup captain Pat Rafter have warned the 18-year-old to channel his ''showmanship'' in a five-set match to ensure he can last the distance in grand slam tournaments.

Big-serving Kyrgios wowed the Australian Open crowd and earned plenty of admirers before he was struck down by cramps in a late-night five-set loss to French 27th seed Benoit Paire in the early hours of Friday.

It has boosted his chances of usurping Tomic as Australia's singles player for the tie against France at the end of the month.

Tomic was booed by fans when a groin injury forced him to withdraw from the Australian Open and it's not clear whether it will keep him out of Davis Cup action.

Kyrgios made his Davis Cup debut last year.

''Nick is very much in the mix of playing Davis Cup and we see him as a real chance of playing again for us,'' Eagle said.

''We'll give Bernie as much time as possible [to get fit] and we'll make a decision.

''But even if Bernie is fit, we're seeing great stuff from Nick and there's no reason why he can't push for a spot.

''He has shown he can mix it with the best in the world, he's definitely a chance.''

Kyrgios dominated the first two sets of the round-two match against Paire, but faded after more than three hours on court and his debut Australian Open came to a halt.

Australian great Rafter said Kyrgios had an X-factor and the ability to play the big points like a seasoned pro.

But the two-time US Open champion Rafter said Kyrgios made ''a few junior errors'' against Paire.

''Like not seizing the moment at the right time, and his body language,'' Rafter said.

''It's fine for the next couple of years to be young and to enjoy himself, but this is men's tennis now and there's a little bit of his strut that we need to control a little bit, just to show respect for the other players.''

Kyrgios lacked match fitness after being hampered by shoulder and elbow injuries since October last year.

His Australian Open hopes last year were also dashed by cramp in the qualifying stages.

Coach Simon Rea said Kyrgios was still learning how to ''regulate'' his emotion in a draining five-set match.

Kyrgios was feeding off a vocal and supportive crowd and played at a frenetic pace to start his match against Paire, winning the first two sets.

He started to cramp in the fourth set and struggled physically at the end of the match.

''I'm really proud of his effort from the first ball to the bitter end, he had a crack right until the finish line,'' Rea said.

''That's a terrific place to start. Nick has that extremely excitable, big personality, showmanship side and he values that.

''We don't want to take it away from him, but he has to learn how to be mindful of how and when he emotionally releases the brakes.

''He was incredible … five-set tennis is a physical and mental test of the toughest kind. He'll have to learn to regulate that, but he'll know that and he's an intelligent young man.''

Eagle said Kyrgios' physical development had ''exceeded expectations''.

Kyrgios played in his first grand slam at the French Open last year and qualified for the US Open.

Eagle urged Kyrgios to focus on physical development rather than rising up the rankings.

''Nick has highlighted his potential and ability to step up in big tournaments against top world-class players, the future looks good, there's no doubt about that,'' Eagle said.

''It's a different beast playing five-set tennis, he'll learn and we're not concerned about that at all.''