Kristian Prenga has been backed to upset Anthony Joshua "like [Andy] Ruiz did" by sparring partner Brandon Moore ahead of their fight on Saturday in Saudi Arabia.
Joshua's first professional defeat came at the hands of Ruiz in 2019, in a monumental upset at Madison Square Garden that saw Joshua lose his IBF, WBA and WBO titles.
Though Joshua - who is fighting Prenga (20-1-0, 20 KOs) as a warm-up bout for his highly-anticipated fight against Tyson Fury in the winter - is heavily favoured against the Albanian, Moore feels that the British heavyweight could be subject to a similar shock defeat in Jeddah.
"[Prenga] looks really, really, really good in sparring right now. It's going to be a pretty entertaining fight," Moore told Sky Sports.
"I think that he has a pretty good shot of beating him, and I think he's bigger than Joshua. Joshua just has a muscular physique, but Prenga's a bigger man.
"It's going to be a tough fight, but I think he can catch [Joshua] the same way Andy Ruiz did.
"This is AJ's first fight back. AJ's had a lot of stuff going on in his life - nothing but respect to AJ, but when you're getting back into the ring, you haven't fought in a while, that ring rust is real.
"This is not a small thing - everybody's going to be watching."
Moore, who is hopeful of his own high-profile bout against a UK heavyweight, was quick to emphasise the value of Prenga's fight against Joshua, which is undoubtedly the biggest of his career so far.
"I told [Prenga] that he has the opportunity of a lifetime. He has the opportunity that I would wish for.
"AJ is a great fighter, and he's done amazing things in the sport of boxing.
"But [Prenga] has the opportunity, you know, to be in the names of people that have beaten future Hall of Famers.
"Everything has to be aligned. He has to do everything perfectly."
Watch Johnny Fisher fight in the Zuffa Boxing event at the Copper Box Arena on Saturday September 26, live on Your Site
