Terry Flanagan has insisted Russian Petr Petrov will be his best challenger yet -- and he may be one of his last at lightweight.

Petrov is not the big name Flanagan had been craving in a career that has yet to make him one of Britain's biggest boxing stars, despite being a world lightweight champion.

But Flanagan [32-0, 13 KOs], 27, still regards Petrov [38-4-2, 19 KOs], 34, as the biggest threat to his reign as WBO champion after four defences.

"I think he's the toughest challenger I've had so far," Flanagan told ESPN. "I saw what he did in the fight against Dejan Zlaticanin [in 2013] and he's tough. He's a fighter and I'm a boxer. A good boxer beats a good fighter and I think I can handle what he's got.

"My last opponents have come up through the weights but this will be tougher because he's in the prime of his career and has had some good results in the States recently."

Providing he is successful at the Manchester Arena on Saturday, Flanagan is being lined up for a bigger fight later in the year against rival world lightweight champion Jorge Linares [42-3, 27 KOs] or Vasyl Lomachenko [7-1, 5 KOs], who defends his WBO world super-featherweight against Jason Sosa also on Saturday.

Even so, Flanagan does not see his long-term future in the lightweight division.

"I think I will end up fighting at light-welterweight next year and even welterweight," Flanagan said. "The weight is not easy to make, but no one finds it easy. At the moment I can make the weight and everything is on track."

Flanagan gained encouragement ahead of the fight from a visit from Billy Graham, who used to train two-weight world champion Ricky Hatton.

"Billy came down to watch me spar and says I'm the best in the division, which is great to hear from someone like him. He says if I keep making the weight I will beat any of them."

Despite Flanagan's ambition and world title status, he has yet to enjoy the attention and following other British boxers get. But promoter Frank Warren is convinced the recognition and popularity will come.

"Terry has got the longest unbeaten record in British boxing right now and Joe Calzaghe was unbeaten and became an 11-year overnight sensation," Warren told ESPN. "It took Joe a long time to get the recognition and Terry can do the same thing."