Tennis: Nick Kyrgios defeated by Alexander Zverev in FAST4 singles, but wins with Lleyton Hewitt in doubles

Nick Kyrgios has allayed pre-Australian Open injury fears with an energetic display at Sydney's Fast4 exhibition tournament.

Kyrgios turned up at Sydney Olympic Park's Ken Rosewall Arena with strapping on his troublesome knee but emerged unscathed from his light-hearted singles loss to Alexander Zverev. He then teamed up with Lleyton Hewitt in the doubles to down Zverev and Bulgarian world No.3 Grigor Dimitrov.

The 22-year-old is being touted as an outside favourite to win his first grand slam at Melbourne Park, having risen to 17th in the world rankings on Monday to become Australia's top-ranked player following Sunday's Brisbane International title.

The injury clouds currently hanging over world No.1 Rafael Nadal, Novak Djokovic and Stan Wawrinka ahead of the Open were clearly not affecting Kyrgios.

"It (the knee) feels okay, it's not bothering me that much," Kyrgios said afterwards.

"I obviously played pretty well last week so it'll be OK."

At least for the time being, Kyrgios may be more focused on nursing a swollen and bloody lip after copping a ball to the mouth from Zverev during the doubles hit and giggle.

As the pair both closed in on the net, the German world No.4 popped a gentle volley straight into the Australian's face before jumping over to playfully cuddle his felled victim.

The notoriously big-talking Kyrgios was briefly lost for words.

"That one hurt," he said into his microphone.

"That was like a jab straight to the mouth."

Dimitrov, who at one point entertained the crowd by jumping into the umpire's box to check a Kyrgios challenge, won his singles match against the retired but lively Hewitt.