Olympic champion Wayde van Niekerk has confirmed a knee injury will rule him out of defending his 400 metres title at the IAAF World Championships.

The 400m world record holder confirmed he would not be fit to take part in Doha when the competiton starts this month, having suffered several setbacks in his recovery from an injury sustained in a touch rugby game back in October 2017.

Van Niekerk has not raced internationally since that incident and the 27-year-old will continue to carefully manage his rehabilitation, with an eye on competing in the 2020 Olympic Games in Tokyo.

"I'm still positive and I'm just taking things day by day, respecting all the calls made by the doctors and respecting my body," the South African, who has returned to training, said in a statement.

"For me it's just about listening to my body and taking it from there. My main goal is to look after my body and when the opportunity comes, I'll take it.

"For now I'm not rushing myself or putting pressure on myself. I'm extremely happy and at peace with where I am."

His doctor Louis Holtzhausen suggested things would begin to look much brighter for Van Niekerk over the coming weeks and months.

"The medical teams, both in Bloemfontein and Aspetar [Qatar], did all we could to have him ready for the World Championships, but it was just not possible," said Holtzhausen in the same statement.

"However, he has successfully returned to track training and all indications are that he will recover more rapidly from now on."