Anthony Crolla views Vasiliy Lomachenko as being close to unbeatable.
Earlier this year, Crolla had a mandatory shot against Lomachenko, and the British boxer was brutally knocked out in the fourth round in a bout which took place in April in Los Angeles.
Next month, Lomachenko will pack up his suitcases and fly over to the UK to fight on foreign soil.
Lomachenko will collide with Olympic gold medal winner Luke Campbell, with the WBC, WBA 'Super' and WBO titles at stake on August 31 at The O2 in Lond, with DAZN and Sky Sports Box Office carrying the fight.
Lomachenko himself has two Olympic gold medals and one of the most impressive records in amateur boxing history. And he's already won world titles in three weight divisions.
"I think he's the complete fighter - speed, defence," Crolla told Sky Sports.
"He hits harder than you expect as well. He varies the power up very well and just so clever, so clever at reading fighters. No man's unbeatable, but he's close to it."
Crolla expects Campbell to do well in the early rounds, but he also expects Lomachenko to eventually make adjustments as the fight plays out.
"I believe it's the toughest test in boxing. I experienced it first-hand," said the former WBA champion.
"I think Luke has the better tools for the job than what I had stylistically, and I think for the first sort of three rounds or so, he might have a little bit of success.
"I think he'll keep it long, but I do believe at some point in the fight, Lomachenko will catch up with him."
