MOSCOW — Looking to stop his stellar career from fizzling out, Roy Jones Jr. takes on Denis Lebedev in Moscow later today.

Jones is challenging Russia’s top cruiserweight to prove his worth: “If you can whoop me, whoop me.”

The 42-year-old Jones has been in decline since his mid-30s, prompting a return to cruiserweight, perhaps as part of a hopeful quest to add the only title to elude him between middleweight and heavyweight.

But the American’s poor form in losing his last two fights to Danny Green and Bernard Hopkins, and the jarring power of his more youthful opponent, have earned Jones the underdog tag.

Jones, who has a 54-7 record with 40 KOs, exuded confidence at Friday’s weigh-in, letting out a roar after officials registered his weight.

“If you can beat me, beat me,” a philosophical-looking Jones told the state television network Russia Today.

Despite the absence of a title at stake, the tension was palpable as Jones and Lebedev stood toe-to-toe, avoiding eye contact.

The 31-year-old Lebedev, a versatile southpaw trained by former undisputed welterweight champion Kostya Tszyu, boasts a 21-1 record. His only defeat came in a controversial decision given to WBO cruiserweight champion Marco Huck in Germany last year.

Lebedev, feared for his knockout power in both fists, started out as a light heavyweight before settling in the cruiserweight division. He has a string of impressive victories while fighting mostly out of Russia.

“When Denis steps in the ring for this bout, I want him to be an aggressive, hungry and aspiring fighter, thinking: ‘I’d rather die than lose.’ That’s the feeling I didn’t have in my last bouts. And neither does Roy now,” Tszyu told Russia Today.

Jones, who once held a record seven belts at the same time and was chosen 1990s Fighter of the Decade by U.S. boxing writers, still likes to display a lighthearted side, performing his rap song “Heart of a Champion” for his Moscow fans.

And he is under no illusions about his age, either.

“I float like a butterfly, sting like a bee,” he joked. “His trainer is just as old as me.”