Genzebe Dibaba, the 2015 champion and world record holder in the women's 1,500 metres, will miss the World Championships due to a foot injury, the Ethiopian said on Instagram.
Dibaba, 28, who won the world title in Beijing in 2015 and set the global best of 3min 50:07sec over the distance the same year, is suffering from a partial rupture to a ligament in her right heel which she suffered during the Zurich Diamond League meeting last month.
"Unfortunately I am not able to be at Doha World Championship. I am already working to come back stronger!" she posted alongside a photo.
The Netherlands' Sifan Hassan, the second quickest woman over the distance in history, is now favourite to take gold in Doha. Kenya's Faith Chepng'etich Kipyegon will also be in Doha to defend her title after making her comeback recently. She won the Kenyan trials for the Worlds.
The championships take place from September 27 to October 6.