Grand slam legend Rafael Nadal has broken up his preparation for the Australian Open by treating his wife Xisca Perello and baby son to a trip on Sydney's spectacular harbour.

The former world No.1 was seen protectively cradling Rafael Junior in his arms as the trio boarded a boat on Wednesday, with he and his son wearing matching white and navy blue outfits for the journey.

They were accompanied by friends and one of Nadal's coaching team, Argentine former professional player Gustavo Marcaccio, as they took in the sights on one of the world's most famous stretches of water.

Rafael Junior was born in October last year and his father spoke about the impact his first child has had on his life and game after arriving in Sydney for the United Cup tournament.

'The first event I play like a father without the baby with me, I lost first round. Second event, traveling with the baby, I was out of the group stage. At the end I won my last match, but I need to keep improving, no?' he said.

'We have some help. No problem at all. Just I need to organise little bit my life, as everybody needs to do when you have a child in your life.'

The Spaniard's form has been rocky since he arrived down under to prepare for his attempt to win a second straight Australian Open title.

He fell to Cameron Norrie and Aussie underdog Alex De Minaur in the United Cup and promptly said the format of the new tournament - which sees national teams compete - should be changed after his loss came during a dead rubber.

'Putting things in perspective [for] this competition, I find a negative point,' the world No.2 said.

'Competition is great. Idea is great. It's not great that today we are playing for nothing.

'It's the first year of this competition, so that's the kind of thing that we need to fix, to improve, and to make it more interesting for everyone.'

Nadal has also been left annoyed as he fielded constant questions from the media about whether he's about to retire.

'I lost my match. That's it, no? Every time I come to a press conference it seems that I have to retire. So you are very interested on my retirement. I mean, that, for the moment, isn't the case,' he told reporters after his loss to Norrie.

'When the day arrives, I'm going to let you know, guys. Don't keep going (on) with the retirement, because I'm here to keep playing tennis.'