Hughie Fury, who lost a twelve round decision in a world title eliminator with Kubrat Pulev, believes the Bulgarian veteran could trouble Anthony Joshua.
Joshua will defend the IBF, IBO, WBA, WBO heavyweight titles against Pulev on Saturday night at the SSE Arena at Wembley.
Pulev has a single defeat on his record, which dates back to 2014 when he challenged then unified champion Wladimir Klitschko.
Pulev, nearly 40-year-old, could prove to be a difficult opponent for the British star, says Fury.
"Pulev is a very difficult fighter. He'll give Joshua problems in the early rounds and then he doesn't need to let him set behind his jab. If he lets Pulev sit behind his jab, he's going to have problems," Fury told Sky Sports.
Fury did notice, during their 2017 scrap, that Pulev's energy saps in the second half of the contest and his defensive abilities begin to die down.
"Don't let him get comfortable. I think Pulev dies out in the later rounds. Obviously I had the cut and I was worn out after putting everything into the third round. In the eighth he started to slow down. His defence was more leaky and that's when I was able to wobble him. But I didn't have the energy to finish him," Fury said.
Fury will see action on the Joshua-Pulev undercard, when he faces Polish giant Mariusz Wach, who lost a ten round decision to Dillian Whyte in Saudi Arabia last December.
The cousin of heavyweight champion Tyson Fury has promised to put on a spectacular performance.
"You're going to see something special. Mariusz Wach has never seen anything like my style. He's been in with everyone but he's never been in with anyone like me. I'm going to take over the heavyweight division one day. Believe me, he's not going to go the distance," Fury said.