Keith Thurman believes Kell Brook must show he is good enough to be among the best welterweights in the division.
Brook is looking to target Thurman for his WBC and WBA belts after defending his IBF belt successfully.
However, Thurman does not think Brook has what it takes to slug it out with the best in the welterweight.
“Of course Kell Brook came over here to America to take the title back home but for this one, he has fluctuated in weight classes,” he exclusively told Sky Sports.
“I am just interested in how bad he wants to be a welterweight and establish himself as one of the best welterweights in the world today.
“It is going to be difficult (moving back down to 147lbs) if he wants to hold onto that title and in my opinion, he didn’t do enough at welterweight before moving up anyway.
“For me, that is what this fight is about. In my opinion, there is so much going on at 147 but he had to go up two weights just to make a big fight happen.”