The former IBF Cruiserweight Champion said he has no interest in dropping back down to that weight class.
Cruiserweight Maccarinelli just beat an eight count before getting to his feet, only to be sent crashing again.
Former undisputed cruiserweight champion Haye, 28, pointed to Klitschko's six title defences as evidence to back up his claims.
Maccarinelli hopes to fight for the WBO cruiserweight belt early next year.
Former world heavyweight champion Herbie Hide continued his cruiserweight comeback with a controversial stoppage of Czech Pavol Polakovic in Hamburg.
Maccarinelli was confident of ruling the cruiserweight world before his battle of Britain with Haye for the undisputed crown last February.
And Maccarinelli's promoter Warren suggested that the Welsh cruiserweight was ill-prepared for his WBO interim title shot in Manchester on Saturday.
Swansea's Maccarinelli, 28, had hoped to be fighting for his old WBO cruiserweight title but had a string of opponents pull out on him.
The cruiserweight showdown will be the chief support to an equally mouth-watering fight at super middleweight between Joe Calzaghe and Jeff Lacy.
London's former cruiserweight world champion David Haye, who made an impressive heavyweight debut against Monte Barrett last month, was ringside in Mannheim.
That belt was held by Maccarinelli until March 2008 when he suffered a second-round knock-out in a cruiserweight unification clash with David Haye.
Former undisputed cruiserweight champion Haye, 28, added that his trash-talking tactics had had the desired effect and he did not regret his actions.
The bout is for the vacant WBO intercontinental cruiserweight title, with the winner expected to go on to challenge for the WBO world title.
It was the second defeat of 31-year-old Haye's 27-fight career, most of it at cruiserweight before stepping up a division for his last five fights.
The 28-year-old, who lost his WBO title to David Haye in March 2008, continues his comeback against Ola Afolabi for the interim WBO cruiserweight belt.
However, that plan seems to be in tatters after Jones was stopped in the first round by IBO cruiserweight champion Danny Green in Sydney on Wednesday.
Commonwealth Games semi-finalist Stephen Simmons is the latest recruit and Nelson is optimistic that the fledgling cruiserweight will turn out to be a valuable addition to his stable.
The former cruiserweight king, who has lost only once in 25 professional bouts, then defended his title by stopping American John Ruiz at the MEN Arena in April.
Haye, who is lined up to face WBC and WBA cruiserweight champion Jean Marc Mormeck in the autumn, also denied rumours of a relationship with singer Kylie Minogue.
Britain's Haye, a former cruiserweight, is Hopkins' most obvious target.
The Swansea cruiserweight, 25, who holds the WBU title, will finally get a chance to enter the big league when he faces WBO king Nelson at the MEN Arena.
Haye's manager Frank Maloney said he would now begin negotiations with Frenchman Mormeck, who holds the WBC cruiserweight crown, with a view to lining up a fight before September.
His first opponent - Belshaw - appeared to be a blown-up cruiserweight who looked uncomfortable in the ring against Harrison, while Hughes caught the 37-year-old with far too much ease.
It was Rees's first defeat in 28 professional bouts and compounded a bad month for trainer Enzo Calzaghe, whose WBO cruiserweight champion Enzo Maccarinelli lost his title to David Haye a fortnight ago.
But Afolabi spoilt his plans for unification world domination to claim the interim WBO cruiserweight belt, taken his record to 14 wins from 17 professional fights with his shock success at the MEN Arena.
London's Haye, 27, destroyed Wales' Enzo Maccarinelli in March to become the undisputed cruiserweight champion and plans to have two fights against top-10 ranked heavyweights before challenging IBF and WBO champion Wladimir Klitschko in 2009.
Corbett previously held the Commonwealth cruiserweight title.
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