Last year, Olympic gold medal winner James DeGale (24-2-1, 14 KOs) went through the worst twelve months of his pro career.
In January 2017, he barely escaped with a twelve round majority draw - when he collided with Badou Jack in a super middleweight unification at the Barclays Center in Brooklyn.
DeGale suffered numerous injuries in the loss to Jack and rehabilitation period kept him out of the ring for most of the year.
DeGale didn't fight again until December 2017, when he lost his IBF world title when he dropped a shocking twelve round majority decision to Caleb Truax.
Some bookies had Truax listed as a high as a 100-1 underdog.
A rematch was set for last month in Las Vegas, and saw DeGale reclaim his IBF belt by winning a razor close twelve round unanimous decision.
Jack believes all of the tough fights have finally broken DeGale's body down.
"I wasn't so impressed [with his win over Truax]," Jack exclusively told Sky Sports. "All the tough fights he's been through, I think he's not the same fighter anymore.
"But he always shows heart, he's got a lot of heart, but I wasn't impressed with his last performance. I think it could have gone either way, or a draw, or maybe even a loss. You've got to give him credit, he shows a lot of heart."
Jack, who now competes at the light heavyweight limit, has no problem with granting DeGale a rematch - if the contest takes place at 175-pounds.
"I love the UK fans, I would love to fight in the UK before I retire," Jack said. "If [DeGale] comes up to light-heavyweight, and he continues to win, maybe yeah.
"But I can't make super middleweight no more, so if you want to come up, sure. You've got to ask him if he wants it."
Jack returns on Saturday night in Canada, when he faces WBC champion Adonis Stevenson.