Andy Ruiz Jr has made it very clear that you shouldn't doubt him because of his physique after posting an impressive recent work-out video ahead of his big fight against Anthony Joshua this weekend.

The Mexican, with a record of 32-1-0, is a late replacement for Joshua's initial opponent Jarrell 'Big Baby' Miller, who failed a number of drug tests back in April.

Ruiz Jr has been heavily criticised for his shape in the build-up to the June 1 bout at Madison Square Garden in New York, but he's been out to prove his doubters wrong.

A video has been posted onto the 'K.O Artist Sports' YouTube channel which presents the 29-year-old's frightening hand speed, proving he's not an opponent Joshua should take lightly even if he is, without question, the clear underdog.

Joshua - the IBF, WBO and WBA champion - has joined Ruiz Jr in ignoring the concerns about the latter's stamina and believes muscles don't mean success in boxing.

Ruiz Jr has stated he's planning on adopting sporting great Mike Tyson's style against the undefeated Brit.

"I’ve seen a lot of weaknesses in him and I’ve seen him working on them. The main thing is to stick to the game plan. I don’t want to say too much about his weaknesses. I’ve just got to improvise and exploit them when the bell rings."

He continued: "We’ve seen a lot of videos of Mike Tyson.

"We’re working on some of the moves he did so I can get to Anthony Joshua.

(Skip to the 2:08 mark in the above video)

"The main thing is we’ve got to stay focused and prepared. Get ready for anything and stay in shape."

Joshua has had 22 fights and won all 22, with 21 knockouts, so it's no surprise he's being heavily touted to put Ruiz Jr down onto the mat on fight night.

His opponent will be hoping he can push him to the limit like Joseph Parker did last March, though, taking it to a unanimous decision.