Spanish tennis great Rafael Nadal has squashed talk of retirement following his shock loss to Cameron Norrie in the United Cup, insisting that he's 'here to keep playing tennis'.

The 36-year-old world No.2 went down 3-6, 6-3, 6-4 to Norrie in front of a large crowd at the Ken Rosewell Arena in Sydney.

It was the fifth time the two players had met and the first time Norrie had won - earning Great Britain its first victory in the tournament over Spain.

The 22-time grand slam winner clearly struggled against Norrie, but took exception to reporters asking about retirement at the press conference.

'For me, I lost my match, that's it,' said Nadal.

'Every time that I am coming to a press conference it seems that I have to retire.

'So, you are very, very interested in my retirement. I mean, for the moment it is not the case.

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

Nadal's shock three-set loss to Norrie, and Katie Swan's upset win over Nuria Parrizas Diaz, gave Great Britain a surprise 2-0 lead over Spain in Sydney on New Year's Eve.

Those results mean Badosa needs to beat world No.98 Harriet Dart and Carreno Busta must get the job done against Daniel Evans to send the tie to a live mixed doubles on New Year's Day.

Nadal is currently listed to play in the mixed doubles, and the tennis legend is no doubt champing at the bit to make up for his opening-match loss.

Great Britain have already beaten Australia 3-2 in the opening tie. If they also defeat Spain, it would mean that neither Australia nor Spain would be able to win the title.

'It's true that the competition, the format, doesn't give you a lot of chances, a lot of room for mistakes, no?' Nadal said.

'Losing my match now we are under a lot of pressure. So let's see.'

Germany are also under pressure after falling 2-0 behind to the Czech Republic.

Petra Kvitova can wrap up the tie for the Czech Republic with a win over world No.27 Laura Siegemund.

Norway trail Brazil 2-0, and the pressure will be on Casper Ruud when the world No.3 takes on Thiago Monteiro in Brisbane.

Belgium and Bulgaria are locked at 1-1 in their tie, as are Poland and Kazakhstan.

Croatia lead Argentina 2-0.

Australia are back in action on Monday, with Alex de Minaur scheduled to take on Nadal and Zoe Hives due to face Parrizas Diaz.