Harrison won the Prizefighter in October
Audley Harrison is to fight Michael Sprott for the vacant European heavyweight title in London on 9 April.
Sprott, who beat Harrison three years ago, is the replacement for Poland's Albert Sosnowski, who pulled out of a proposed title bout earlier this month.
The 31-year-old Sosnowski withdrew after he was offered a world title shot against Vitali Klitschko.
In October the 38-year-old Harrison knocked out Scott Belshaw to win the Prizefighter heavyweight tournament.
That victory earned the 2000 Olympic champion £32,000 in prize money and a contract with Matchroom Sport promoter Barry Hearn.
Sprott, 35, won by a stunning third-round knockout when he met Harrison for the European crown in 2007, but the Bedford fighter has lost four of his last six fights.
And former Olympic gold medallist Harrison insists he will hang up his gloves if he loses against Michael Sprott at Alexandra Palace.
"I'm calling this revenge or retirement," said Harrison. "If I can't get revenge over Michael Sprott then my career can't go forward.
"If I can't beat him then there's nowhere else to go. That's the mentality I'm going in the ring with - I have to go and win this to move to the next level.
"I will retire if I don't win this so we know what's going to happen - I'm going to win this fight, no doubt.
"I've been looking forward to avenging that defeat and the fact it's for a European title is a double boost for me.
"Albert Sosnowski didn't even defend his European title and he only won it in December, so fighting for a world title is definitely a reality for me.
"Everyone is talking about the Klitschko brothers [WBC champion Vitali and IBF/WBO champion Wladimir) so these are the guys that I will be targeting.
"I would love to fight [WBA Champion] David Haye but... the real champions are the Klitschko brothers."