Clarke is a regular sparring partner of Joshua and has just returned from the biggest success of his amateur career, winning super-heavyweight gold at the Commonwealth Games in Gold Coast.
Joshua meanwhile is in the process of trying to make a heavyweight unification fight with Deontay Wilder, with further talks due to take place at the end of the month after the American rejected an £8.8million offer.
The Brit is unbeaten in 21-fight professional career and has only once been dropped, by Wladimir Klitschko in their epic fight at Wembley last year.
However, promoter Frank Warren claims his young 7-0 heavyweight Dubois has dropped Joshua, something Clarke believes cannot possibly be true.
“I have never seen him put Joshua down,” Clarke told Sky Sports.
“I am sure I am at 99 per cent of the spars and it has hit him flush and has probably shook him up a bit, but the way they make out that he put him down on his backside, it just never happened.
“I don’t think it was Daniel, it’s the people around him. Daniel is a nice kid and he probably admitted he shook Joshua up a bit in sparring and someone has made more of a story of it.
“I can honestly say if it was true, Joshua would turn round and say ‘yeah, it happened, it was true’, but he hasn’t.
“Don’t get me wrong, it’s sparring and people take big shots and I have seen him [Joshua] take a big shot off Daniel and I’ve seen him give Daniel a big shot.
“I’ll tell you first hand he [Dubois] can whack really hard.
“Everyone gets put down in the gym and I am not afraid to admit it and he knocked me down.
“He caught me with a shot, half off-balance, and he is a heavy-handed guy but you just get back up.”
At 6ft 5in, Dubois is viewed as the kind of fighter who could challenge the likes of Joshua, although he is yet to face opposition of any real quality.
The 20-year-old picked up the Southern Area heavyweight title on his last outing, stopping DL Jones in the third round of their contest.
And Warren wants to take his time with the fighter, despite his alleged exploits in the gym.
“Look, I don’t go crazy about young fighters because there is always a long way to go – but he is by far the best heavyweight at this stage of his career that I have seen in my time in boxing,” Warren said last year.
“He has a fantastic jab, real power, he’s relaxed, a natural boxer and puncher.
“Not only did he knock Joshua down [in sparring], he absolutely did for Joshua in the gym, as he has done with all the names he has sparred with.”
Source : EXPRESS