Wöstmann revealed on Monday that she had not fully recovered from the hamstring injury she suffered at last month’s Two Oceans Marathon.
“Despite aggressive recovery treatments and rehab to the injury it hasn’t healed sufficiently to allow me to safely compete at Comrades this year,” Wöstmann said in a statement.
“On Sunday the 4th of June 2017 I won’t be running the Comrades Marathon but I will be one of the supporters," she said.
“Even though everything in me wants to go and run Comrades, I have made the heart-breaking decision to listen to my medical team and withdraw from the race.”
Wöstmann has become one of the darlings of South African ultra-running since winning the 2015 Comrades Marathon title in a time of 6:12:22.
She became the first South African winner of the Comrades Marathon since Rae Bisschoff in 1998, and was only the fourth person to also win the Two Oceans in the same year.
The 34-year-old Wöstmann made a promising start to her season defending her Om die Dam Ultra-Marathon in March.
At last month’s Two Oceans Marathon, the two-time defending champion pulled out of the race just after the 11km mark due to a hamstring injury.
“During Two Oceans I picked up a hamstring niggle where it was later diagnosed as a neural injury which was far more serious than originally presumed,” Wöstmann said.
“I want to thank all my sponsors, my team and my friends for their incredible support.”
At the 2016 Comrades Marathon, Wöstmann looked set to successfully defend her title before cramps and injury took its toll with 10 kilometres to go.
Erasing an 11-minute gap, Charné Bosman moved past Wöstmann with two kilometres to go to the Kingsmead Stadium finish line to claim the title in a time of 6:25.55.
Although Wöstmann will not be lining up at the start for the 2017 edition of the Comrades Marathon, she will be giving her support on the day.
“I have received so much energy and motivation from the Comrades supporters cheering me on in past years and I hope I can give that back to my fellow Comrades as they complete their journey this year,” Wöstmann said.
“I wish every one of my Comrades a life-changing adventure from Durban up to Pietermaritzburg this year.”
Defending champion Bosman will be leading the country’s charge among a strong international challenge.
The 41-year-old finished as runner-up in 2015 and is fresh off a second-place finish at the Om Die Dam Ultra-Marathon.
Bosman can expect a strong challenge from veteran four-time Olympian Colleen de Reuck, who finished in seventh place on her Comrades debut last year.
Former World 100km and 50km champion Camille Herron of the United Sates seems to be hitting form at the right time.