Joshua Cheptegei is yet to run his first marathon but two-time Olympic champion Eliud Kipchoge believes the Ugandan could become the world's fastest man over 26.2 miles.

Cheptegei won 5,000m gold at the Tokyo 2020 Games and holds the world record for both that distance and the 10,000m.

His Kenyan inspiration, Kipchoge, is now backing Cheptegei before the 27-year-old's marathon debut in Valencia on Sunday.

"He is already a record holder in other fields and he has a huge chance to break a world record in the marathon," Kipchoge told BBC Sport Africa.

"Joshua is talented and disciplined. He is learning well.

"I am happy Joshua is trying a new venture. I will be watching and giving my moral support as always."

Cheptegei is regarded as one of the best distance runners in the world, with three 10,000m world titles and a world cross country title alongside his Olympic gold.

He previously held the world records for the 5km and 10km road races and trained with Kipchoge, who broke the marathon record twice, in 2015 in Kaptagat.

The Kenyan says Cheptegei's "growth" has derived from the various distances he has run, but the 39-year-old has advised the Ugandan to run his own race on Sunday.

"Kipchoge inspired me a lot when I was starting up my career, his legacy inspires me," Cheptegei said.

"His kind words have always been able to shape me over the days and years. Eliud is always keeping an eye on me, always guiding us in a good way.

"It's a great honour to learn from the great. For this special regard, I'm looking forward to putting into use what we always share together."

As he steps into the unknown and a different running rhythm, Cheptegei says he will give the marathon the respect it deserves.

"Marathon has no respect for persons. I want to approach this marathon with a lot of respect because it is something that is very new to me," he added.

His coach Addy Ruiter says Cheptegei must be wary of pressure, with his track events at next year's Olympics in Paris still in mind.

"This debut is especially for learning how the body and mind adapt to marathons," Ruiter said.

"The focus for next year is the 10,000m at the Olympics - because of the new generation of running shoes (Cheptegei will use Vaporfly) we could do this also without it affecting his preparation for Paris.

"When I look at his preparation, a time of two hours and three minutes to two hours and three and a half minutes is realistic.

"I'm sure he can run much faster than that, but that's something for after Paris and then he has to focus 100% on the marathon."

Cheptegei is Uganda's greatest athlete, with a career spanning a decade, and he won his first world title - the 10,000m junior crown - in 2014.