Kell Brook says he will fight Errol Spence -- his new mandatory challenger -- only if fight fans demand it.
The Briton steps up two weight divisions to take on Gennady Golovkin for his three world middleweight title belts in London on Sept. 10.
But Brook (36-0, 25 KOs), 30, has not ruled out returning to welterweight to defend his IBF world welterweight title -- win or lose against Kazakhstan's U.S.-based Golovkin, who is ranked No.2 in ESPN's pound-for-pound rankings.
American Spence (21-0, 18 KOs), 26, became Brook's mandatory challenger with a clinical sixth round win over Leonard Bundu Sunday.
"I think I will defend my title again but it all depends on what is the biggest fight out there for me," Brook told ESPN. "I'm not going back just to fight anyone, I want to fight people the fans are excited about.
"I want to be in huge fights. I've become world champion and now I get excited by fighting the best out there, so I will only go the weight where the big fights are.
"Errol Spence would be a big fight and he's tipped to do great things. There would be big interest in me fighting him in the US and he's my mandatory so that's a fight that could happen. If people want to see that fight, I will do it."
Italian Bundhu, 41, took Keith Thurman the distance for the WBA interim title two years ago and had not been stopped as professional until he ran into Spence, who turned professional after the 2012 Olympics after failing to earn a medal.
"I want a shot at Kell Brook as soon as he's done with Triple-G," Spence said. "If he's not going to fight me then he needs to vacate and I'll fight somebody else. I definitely want that IBF title shot this year."