Controversy has marred the Dubai Tour after leader Marcel Kittel was punched by rival rider Andriy Grivko.

The incident, which has earned the Ukrainian a disqualification from the competition, occurred during the 200km stage of the race from Dubai to Al Aqah.

Grivko's Astana team has issued an apology to Kittel and his Quick Step Floors team, but the German sprinter has posted a tweet declaring that he will not accept it.

"I won't accept an apology. That has nothing to do with cycling," he wrote. "What Grivko did is a shame for our beautiful sport."

Kittel was pictured with a bloody face after completing the stage, but managed to maintain the overall lead.

Grivko defended his actions on social media after the race, insisting that he hit out in retaliation after Kittel pushed him and teammate Dmitriy Gruzdev.

He also accused the German of spitting at him.