The US Open tennis champion Serena Williams and French Open champion Ana Ivanovic have withdrawn from the WTA Championships in Doha.
Williams blames a sore stomach muscle while Ivanovic is suffering from a virus.
After beating Dinara Safina and losing to sister Venus, Williams needed to defeat Olympic gold medallist Elena Dementieva to qualify for the semi-finals.
Spectators were not left without matches, as Williams was replaced by Russian Nadia Petrova and Poland's Agnieszka Radwanska replaced Ivanovic.
