The 85-year-old - who has hosted the BBC dancing competition since it launched in 2004 - will be replaced by Claudia Winkleman , who co-hosts the results programme.
The BBC said: "Sir Bruce Forsyth has the flu and therefore isn't feeling well enough to present tomorrow's Strictly Come Dancing on BBC1.
"The show looks forward to his return next week."
Producers regularly schedule rest weeks into Brucie's schedule during the series to help him cope with the workload of fronting three months of weekly live programmes.
Saturday night's show will see the 15 celebrity couples facing the public vote for the first time. Viewers will learn which couple will be the first for the chop during Sunday's results show.