The rematch has been mooted for later this year, with a return to New York's Madison Square Garden a possibility.
The 29-year old Mexican boxer stunned Joshua to win the IBF, WBA and WBO titles on June 1st, with a rematch being scheduled to take place in the latter part of the year.
Andy Ruiz Jr is adamant he beat Joseph Parker in their 2016 world title fight.
Following the defeat, it was announced that the rematch clause in the contract was triggered.
The heavyweight rematch, which is thought to be taking place later this year, is a shot at redemption for Joshua, who was humbled by the surprise victor Ruiz Jr on June 1.
"I'm gonna be more prepared, more ready".
In the aftermath, he said: 'I know his flaws.
The self-proclaimed "Gypsy King" dismissed Ruiz Jr's heroic performance at Madison Square Garden by branding him a "bum".
"First of all I bought a auto for my mum, that was the first purchase I made from the money I got", he said. I don't know if people want me to talk bad about him, but that's not the type of guy that I am. You know a lot of people, and I'm speaking to Joshua too, because he was overlooking me and saying.