Sonia O'Sullivan, who was due to run for Australia at the Commonwealth Games, has lost her battle to overcome a hamstring injury.
The 36-year-old former world champion has pulled out of the women's 5,000 metres set for Friday.
O'Sullivan obtained an Australian passport in January, making her eligible to represent her second country at the Games. But after consulting with her coach and partner Nic Bideau, she decided that she would not recover in time for the race.
The Irishwoman was granted dual citizenship last month and intends to compete for Ireland in the European Championships later this year.
She was granted permission to compete for Australia at the Games despite plans to change eligibility rules in Melbourne. Under normal rules she would have to wait three years to be alllowed to compete for another country.
