Unsung outside the boxing world, a Thai fighter nicknamed the "dwarf giant" is quietly closing in on Floyd Mayweather's undefeated 50 fight record and with it an unlikely place among the sport's greats.

At 1.57m and weighing just 47.6kg, minimumweight Wanheng Menayothin is shorter, leaner and significantly less wealthy than "Money" Mayweather, the undefeated five division world champion who was teased from retirement last year by a $100 million purse to fight MMA star Conor McGregor.

But this spring Wanheng could tie Mayweather's 50-0 record and enter boxing lore.

His 50th bout in April or May is set to be against Panama's Leroy Estrada in Thailand, a low-key affair that will be followed by fans and boxing enthusiasts, but not the global audience drawn to the cross-discipline spectacle between Mayweather and McGregor.

The milestone is generating boxing buzz in a country that is better known for Muay Thai, the kingdom's boxing-style martial art that also allows kicking, kneeing and elbows to the head.

"Am I proud? Yes I am, for being on par with the superstars," the softly spoken 32-year-old said while sitting on a tyre and wrapping his fists with gauze ahead of a training session at his Bangkok gym.

His record of 49 wins with 17 knockouts has been earned against relative minnows - many of them regional fighters - but he has been dominant in the minimumweight division and holds the World Boxing Council belt.

With his present stats he has already matched the legendary fighter Rocky Marciano, but he doesn't dwell too much on the numbers.

"I never thought about breaking records. I just want to win every fight like all athletes who don't want to lose. Keep winning until I quit."

Wanheng is from Thailand's poor rural northeast.

Growing up he viewed fighting as a way out of poverty and moved to Bangkok at age 12 to train.

"When he arrived, he didn't have the best skills, but he got to that point with determination," gym owner Chaiyasit Menayothin said.

Wanheng's legal name is Chayaphon Moonsri.

But like many fighters in Thailand, in both boxing and Muay Thai, he has several nom de guerres for the ring in a nod to sponsors, gyms and his own style.

His endurance in bouts combined with his size earned him the label "dwarf giant", while his alias Wanheng Menayothin derives from the gym owner's name.

To add to the confusion, a promotional tie-in sometimes sees him add "Five-Star Grilled Chicken" to his title because of a sponsorship deal with a Thai food giant CP.

Down a quiet Bangkok road fringed with palm fronds, Wanheng's gym is in a large shed partially exposed to elements, with a ring, weights, rows of equipment, two cats and the occasional intrusive bird.

Wanheng started out in Muay Thai but made the career change as he was running out of opponents, according to the gym owner.

But the move to boxing can also bring a higher-profile and more prize money.

In preparation for the historic 50th bout, trainer Supap Boonrawd, 54, is working Wanheng hard through intense daily sparring and fitness sessions and the thud of punches landing on heavy bags fills the humid gym.

"It will be a moment of pride for him and the whole country too," Supap said of the possible 50th victory.