DJ Mark Goodier - the voice of CD series Now That's What I Call Music! - has suffered a stroke, his production company said.
The former Radio 1 disk jockey is recovering at home following the illness at the beginning of November.
Goodier, 55, will be unable to record the voice-over for Now 95 adverts - a job he has done since Now 20 was released in 1991.
An out of office reply to his email address at production company Wisebuddah said: "Thank you for your email.
"I am away from work for a time recovering from a stroke and so not seeing email every day".
Xtra Factor's Matt Edmondson will voice the Now 95 advert in his place, it has been announced.
Goodier, who presented Radio 1's Sunday night chart show for around 10 years until 2002, is said to be receiving "excellent" medical attention.
It is hoped he will return to work before the end of December, Wisebuddah said.