Kell Brook's promoter Eddie Hearn says the Sheffield fighter's clash with Vycheslav Senchenko will be "by far the toughest test of his career".
Brook will put his unbeaten record on the line when he goes up against the experienced Ukrainian at the Motorpoint Arena in his home town on Saturday.
The 27-year-old, who stopped Carson Jones last time out, is hoping to hold onto his status as the No 1 challenger to the IBF welterweight title, which is currently held by Devon Alexander.
Three separate dates were scheduled for a potential world title clash between Brook and Alexander but injuries to both boxers meant that the contest was called off on each occasion.
"He's had a tough time with the foot injury against Devon Alexander and then Alexander pulling out himself," Hearn told Sky Sports News.
"Kell worked hard to get that No 1 position in the world to take on Devon Alexander, and his world came tumbling down.
"So he rematched Carson Jones to get him out (of the way) and now he faces by far the toughest test of his career in Vyacheslav Senchenko. British fans will remember him for ending the career of Ricky Hatton.
"He's a former world champion himself and has only ever lost to Paulie Malignaggi on cuts. It's a big, big test for Kell Brook and, of course, the No 1 position in the IBF is at stake."
Hearn admitted that Brook did "fall out of love with the sport" after the Alexander debacle but insists he is now back at the top of his game.
If Brook manages to beat Senchenko he will once again be in line for a shot at Alexander or Shawn Porter, who fight for the IBF crown at the end of November.
"He's flying at the moment - he needs to be against Senchenko. If Kell's not 100 per cent in this fight, I don't believe he'll win the fight," Heard said.
He added: "Kell is the No 1 challenger in the IBF, we could have sat back and had an easy fight.
"But he doesn't want to, he wants to be tested, I want to see him tested and the public wants to see him tested.
"So we take on a great fighter in Senchenko, he's got a big team of support with him and a great team of trainers, promoters and managers.
"They've come from Ukraine - they don't like to come out of Ukraine, they came for Hatton and won - and they're here to win. They want that No 1 position, they want the shot at Devon Alexander and Kell Brook has got to hold onto his place."
Brook v Senchenko and a packed undercard including Anthony Joshua, Callum Smith and Brian Rose, is live on Sky Sports 1 HD from 8pm on Saturday.