Names such as Tony Thompson, Lucas Browne and Ian Lewison had been mentioned as possibilities, but it is the 6'7.5", 21-stone (294 lbs) man from Belarus who has got the nod.
Ustinov was already in the country having worked as Chisora's sparring partner—ironically he was the man against whom Chisora broke his hand, thus precipitating the switch.
This is a much better fight than you might expect at such short notice, and the Belarusian has a very respectable record of 29 wins, only one defeat and 21 stoppage victories.
He is clearly a level above Lewison, while Browne and Thompson would have to fly in from Australia and the US, respectively, with the inevitable effects of jet lag.
Although Thompson is well-known in Britain for twice beating David Price and unsuccessfully challenging Wladimir Klitschko on two occasions, he looked overweight and underwhelming in his appearance in Paris last month against Carlos Takam.
Browne, a rugged puncher, may have made for the most potentially entertaining fight, but UK fans will have the chance to see him in action next Friday in Wolverhampton on the Frankie Gavin undercard.
With his huge frame, Ustinov will pose the unbeaten Fury a very different challenge than Chisora.
Here are the key questions going into Fury vs. Ustinov.