He is from K2, the boxing company owned by Klitschko brothers Wladimir and Vitali, the two heavyweights who have stood astride the division for many years, almost rendering it lifeless as they have seen off all comers, credible and otherwise. Their rule has meant heavyweight boxing at the top level has often become predictable.
There lies Tua's strength. He would be a challenger from off the charts. All he has to do to have the possibility of a title shot is beat Ustinov. That's all?
Ustinov has had 28 fights (21 knock-outs) to one loss - to well-performed Bulgarian fighter Kubrat Pulev who is the No1 IBF challenger and highly rated by the WBC and WBO.
Ustinov has also beaten Tua's latter-day nemesis, the lanky US heavyweight Monte Barrett - against whom Tua has a no-win record with a draw and a loss. Ustinov is a man-mountain and Tua has often had problems with taller heavyweights.
Some may scoff at the idea of another Tua comeback. He is 40 and his last appearances in the ring saw him knocked down for the first time in his career in his first fight with Barrett in 2010; a bout he was lucky to draw.
Then, at the rematch, a sluggish and clearly unfit Tua failed to knock Barrett out as he slipped to a points defeat in 2011.
It looked like the end. Pictures were published of a Tua who had ballooned in weight. He didn't commit to the R word (retirement) but others consigned him there.
Barrett was of a type who had given Tua problems before - tall, with a long reach and the ability to move and slip punches. Barrett was also nearing the end of his career. Now 41, his last fight was a year ago when he lost to Shane Cameron. Tua has lost to other boxers of similar style - notably his one world title fight against Lennox Lewis in 2000.
However, David Higgins, of fight promoters Duco, said: "I think a lot of people will make the mistake of thinking that Ustinov is tall, like Lennox Lewis and look what Lewis [1.96m] did to Tua. But just because he is tall doesn't mean Ustinov has the skills of a Lennox Lewis. Tua went 12 rounds with Lewis - he didn't knock him out and David gave him one or two frights."
Having said that, Higgins made it clear that Ustinov is no Nikolay Valuev - the 2.11m, 150kg giant who became the biggest champion in boxing history when he won the WBA title in 2007. However, the massive but slow Valuev was no artist in the ring; he retired in 2009 after being outpointed by Britain's David Haye - a much smaller (1.91m, 95kg) fighter who gave him a bit of a boxing lesson. Haye then lost the title to Wladimir Klitschko (who also has the IBF and WBO crowns; the WBC title belongs to Vitali).
"Ustinov is also a kickboxer and mixed martial arts fighter," says Higgins. "You need some snap and some flexibility to be a kickboxer. He's not a lumbering oaf or anything like that. He has good co-ordination and both these guys have real knockout power."
However, Ustinov was widely panned for his loss to Pulev, with the much sharper Bulgarian winning all rounds before an 11th-round knockout against a fighter reckoned not to have Pulev's movement or ringcraft. Ustinov, however, wobbled Pulev in the seventh round with a big punch.
It should also not be forgotten that Tua has lost only four times in a 58-fight career - to Barrett, Lewis, the highly skilful fast-hands fighter Chris Byrd (who beat Evander Holyfield, Vitali Klitschko and went 12 rounds with Wladimir), and that legendary all-in 1997 brawl with Nigerian Ike Ibeabuchi, who could have gone much further had mental and personal problems not derailed his career.
That is a record any boxer would be proud of and the key to Tua's comeback this time will be whether he is in the right mental and physical shape to do some damage. Against Barrett, Tua seemed to have lost some firepower. That raging left hook seemed to have faded.
Higgins said: "Don't worry, David's last act in the ring was to break Barrett's jaw. Barrett told us later that it one of the hardest punches he'd ever had to wear - and it fractured his face in several places. Have a look at some of the champions David has knocked over when he has been fit and focused: Michael Moorer, John Ruiz, Oleg Maskaev. Tua storms out there and pulls the trigger."
