World road champion Peter Sagan will add some glamour to the Olympic cross-country race this weekend, having gone back to his roots for a crack at Olympic mountain biking gold.

A former world junior champion in cross-country, Sagan has carved out a glittering career as a road racing professional, winning the Tour de France points category five years in a row and the rainbow jersey in Richmond, Virginia, last year.

There was surprise when the Slovakian, 26, decided against competing in the Olympic road race and world cycling president Brian Cookson suggested he might have been kicking himself after Belgium's Greg van Avermaet won gold on the Copacabana.

Sagan is happy with his decision though, saying riding a mountain bike is much more fun than his usual road machine.

"Mountain bike is something different," Sagan said this week after jetting in to Rio. "No one knows what the hell to expect. But it's going to be fun."

Sagan has been training in Park City, Utah, this season, working on his mountain bike technique.

Sunday's race will take place on a bumpy, twisty 4.85km course, featuring a 1km climb and various obstacles.

The men's race makes seven circuits with the race likely to last roughly one and a half hours.

Sagan is used to spending four hours in the saddle on World Tour stages, but says the technical terrain will help him.

He has observed the course this week and liked it, although he was playing down his chances.

"I don't hope for anything. I have not raced mountain bike in seven years. A lot of things have changed," he said.

"I'm here for more personal reasons. I want to try. I don't expect nothing big.

"The parcours can be good for me. Technically I am not bad. I am not here to lose. Can I win? If I lose, I am not disappointed. If I win, it's so good. I'm here for a result. I'm here to give my best."

Sagan's main rivals include world champion Nino Schurter of Switzerland.