Connie Fisher, the star of West End hit The Sound of Music, is to reduce her workload on the advice of her doctor.
Connie Fisher has received rave reviews for her performances
She will now perform six times a week, with Aoife Mulholland - who has been appearing in Chicago - stepping in on Monday nights and Wednesday afternoons.
Mulholland was among those beaten by the Welsh actress in BBC talent contest How Do You Solve a Problem Like Maria?
Fisher has returned to her role as Maria at the London Palladium after a fortnight off with damaged vocal cords.
When she won the role in Andrew Lloyd Webber's production, she vowed to carry the whole show herself.
Her performances earned her awards in the newcomer categories at the Theatregoers' Choice Awards and the London Critics' Circle.
But she fell ill at the start of March, leaving fans disappointed - especially as her absence coincided with that of co-star Lesley Garrett, who was taking part in TV's Celebrity Fame Academy.
Fans were told they could swap their tickets for alternative dates if they were unhappy at missing the show's stars.