Breakfast show host Sara Cox has lost almost 1 million listeners from her BBC Radio 1 audience in a year.
It is one of the biggest slumps for the breakfast show and a setback for Cox, who had to contend with competition from the World Cup for at least one month of the survey.
Radio's golden girl - whose show was rapped for a smutty live interview with Ali G earlier this year - saw her audience slump as the station overall lost 1 million listeners compared with the same three month period last year.
Last year BBC Radio 2 - which today recorded a record high of 13 million listeners - overtook Radio 1 as the nation's biggest station.
Radio 1 executives today blamed the downturn on interest in the World Cup and a general decrease in audiences across most radio stations.
Cox has enjoyed huge audiences since she was brought in to succeed Zoe Ball, thriving on her racy humour and "ladette" image.
However, figures released today by research company Rajar show her show went down from 7.8 million to 6.9 million year-on-year for the three month period from March to June.
However, the BBC pointed out that the 900,000 drop included all listeners over the age of four - it dropped 700,000 listeners over the age of 15.
Measuring the older audience category is the industry standard, but in the past Radio 1 has, to the irritation of the commercial sector, made great play of its total audiences including under 15s.
They have said this is more representative of the station whose audiences include young teenagers.
Radio 1's overall audience also dropped from 13.8 million to 12.8 million in the same period.
A spokesman for the station - which targets 15- to 24-year-olds - said: "During the World Cup there were lots of matches on when Sara was on air. But she still has the biggest youth show in Europe."
Three months ago Terry Wogan's Radio 2 programme overtook Cox for the first time to give him the biggest breakfast show in the UK, based on the standard 15-plus figures.
