The 25-year-old star is expecting her first baby next year and has been told not to perform at Elton's AIDS Foundation event so the Rocket Man will be singing himself now.
According to UK newspaper The Sun, a spokesman said: 'Lily regrets that she has had to pull out of her scheduled appearance this Saturday due to a viral infection.
'As Lily is pregnant and not able to take medication, she has been advised to rest until the infection clears.
'She apologises to Elton and to anyone attending the event which is held to benefit the Elton John AIDS Foundation.'