5 best undefeated champions outside the UFC right now

#2. Reinier de Ridder – ONE middleweight and light heavyweight champion

Reinier de Ridder is among the most dominant champions in all of combat sports today and currently reigns over two divisions in Asia's premier martial arts promotion.

De Ridder has world-class Brazilian jiu-jitsu, with 10 of his career wins coming via submission. Additionally, with every passing fight, his striking has continued to improve.

His professional record stands at 15-0. Every opponent he's faced has struggled against his well-rounded skill set. Strikers are seemingly scared to engage him out of fear of a takedown, while wrestlers are petrified of his impeccable grappling skills.

De Ridder has reiterated his claim to being the best middleweight in the world on numerous occasions, publicly stating that he would easily beat his UFC counterpart, Israel Adesanya.

While Reinier de Ridder is an excellent fighter, there are question marks as to the quality of the opposition he's faced so far in his career. ONE Championship doesn't have the deepest roster and the Dutchman's most notable wins have come against former champion Aung La N Sang.

Meanwhile, Israel Adesanya has beaten world-class fighters like Yoel Romero, Paulo Costa, Marvin Vettori and Robert Whittaker in his career. However, there is a major point of difference between Adesanya and de Ridder.

The ONE titleholder is arguably the better pound-for-pound fighter, considering his success in higher weight classes. Still just 31, de Ridder has a long way to go in his career.

Watch the highlights of Reinier de Ridder's rise below:

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#1. Kayla Harrison – Two-time PFL women's lightweight champion

Kayla Harrison is inarguably the best female MMA fighter outside the UFC. While Harrison primarily competes at 155 pounds, she has fought at 145 pounds in the past. With the UFC's featherweight division currently in an abysmal state, she could singlehandedly rejuvenate a whole weight class if she joins the UFC.

For now, though, Harrison is set to resume her dominant run in the PFL, where she has emerged as one of the highest-paid MMA athletes on the planet, irrespective of gender.

There were rumblings in the MMA community that Harrison would join either the UFC or Bellator after her previous contract with the PFL expired. She ultimately re-signed with the promotion and looks set to further extend her perfect professional record of 12-0.

While her skills are unilaterally respected by her peers, she'll likely never be acknowledged as the best female fighter in the world until she joins one of the premier MMA organizations.

The former two-time Olympic gold medallist is still just 31-years-old. If she sees out her current deal with the PFL and remains undefeated, the opportunities are endless.

Her legacy is in her hands – does she want to continue making significantly more money than her peers, or does she want to go down as one of the greatest female fighters to ever grace the cage? Time will tell.

Watch a compilation of Kayla Harrison's finishes in the PFL below: