Karl Stefanovic has insulted tennis star Daniil Medvedev by bizarrely calling the Russian Australian Open title threat 'Danielle'.

The Today show host attacked the World No.8 when chatting to Aussie tennis player John Millman on Friday morning.

'Danielle, as we like to call him on the Today show,' the TV veteran said.

'He has a mixed bag of fans, [for me] his celebrations [on court] are a little over the top.'

Millman, 33 - who lost to Medvedev in straight sets earlier this week at Melbourne Park - disagreed with 'Karlos'.

'I don't think so,' he responded.

'We need a few characters in our game and he [Medvedev] is one of them.'

Medvedev raised eyebrows following his unusual celebration after beating Millman on Wednesday night.

The former world No.1 sealed the match with an ace and then rolled up his shorts to reveal his upper leg muscles.

Medvedev explained afterwards that the match had left him 'pretty tired', so revealing his leg was a demonstration of his excellent fitness levels.

The Russian also said that he was having a laugh at how his physique compares to that of Hungarian Marton Fucsovics, who stripped off in an intense celebration after beating Federico Coria in the first round.

After his four-hour five-set match on Court 17, the Burberry model removed his fluorescent yellow shirt to reveal an extremely ripped physique, flexed his muscles and yelled out triumphantly.

'That was kind of to show... how I also felt about probably a lot of people on social media,' Medvedev said.

'Photos of Marton after his match... I think I'm just a little bit less muscles than him, so it was also to laugh about myself...I do think I have a little bit of muscles, but definitely not too much.'