Andy Ruiz Jr has warned Anthony Joshua he will be 'lighter, faster and more powerful' when they go face-to-face again in the ring on December 7.

The Mexican floored Joshua four times in New York in June, resulting in one of the all-time shocks in Heavyweight boxing history.

And Ruiz has been working hard as they get set to do battle again in Saudi Arabia before the end of the year, recently showing off a new, leaner side to his physique.

Andy Ruiz Jr has been showing off his new, leaner physique on his Instagram account

The Mexican shocked the world when he floored Anthony Joshua three times in June

With just under two months to go until their highly anticipated rematch, Ruiz informed Joshua that he is working to be in better shape then when he beat him in New York.

'I have a lot of respect for Anthony, outside the ring he is a very good man', he told ESPN Deportes.

'But inside [the ring] there are no friends, there is no respect or anything.

'It will not be an easy fight. I think it will be a hard fight, but nothing is easy in life, so we are training very hard. We will be prepared for whatever he bring.

'I will arrive in better condition.... lighter, faster and more powerful. They will believe that in December they will win.

'People will always talk like this, but I have faith that we're going to win and shut up more mouths.'

Ruiz floored Joshua four times in their June fight, in one of the all-time heavyweight shocks

Ruiz and Joshua face-off last month during a press conference promoting the rematch

Ruiz, 30, was a late replacement for June's fight, after Joshua was originally scheduled to fight Jarrell Miller before the American failed three different drug tests.

When Luis Oritz refused to fight Joshua, Ruiz stepped in a month in advance, with virtually no one in the boxing world giving him any hope of an upset.

But the Mexican captured the WBA (Super), IBF, WBO and IBO world heavyweight titles with his seventh-round TKO victory - Joshua's first defeat in his professional career.