Perri Shakes-Drayton has returned home from the World Championships in Moscow for further assessment on her knee injury and so will not race in the 4x400 metres relay, UK Athletics has confirmed.
The 24-year-old sustained the problem during yesterday's 400m hurdles final in which she finished seventh.
The Great Britain team for this morning's relay heat is Eilidh Child, Shana Cox, Margaret Adeoye and Christine Ohuruogu.
The news is a blow to the relay squad, who have high hopes of a medal at the Luzhniki Stadium.
Shakes-Drayton is the second fastest British woman over the flat this season, behind individual 400m gold medallist Ohuruogu, with a personal best of 50.50 seconds.
She anchored the British quartet to gold, ahead of the United States in the 2012 World Indoor Championships.
The Londoner's coach Chris Zah has accompanied her on the flight home, where the injury, which is to her left knee, will be fully examined.
She had an ultrasound scan last night, having said after the race it "felt funny". It certainly hampered her running badly as she hit hurdles and lost her rhythm entirely as she clocked her slowest time of the year.