While she and her partner Graziano di Prima will not be dancing this week, they are expected to return the following week for the quarter-finals.
A Strictly spokesperson said: "Kym Marsh has tested positive for COVID. As a result, Kym and Graziano will not be taking part in Strictly Come Dancing this weekend.
"Strictly Come Dancing protocols mean that all being well, they will return the following week."
This year's quarter-finals, when Kym and Graziano are next expected to take to the dancefloor, will also double as the show's popular Musicals Week.
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Last Saturday, Kym and Graziano danced the Paso Doble to Only Girl (In The World) by Rihanna / We Found Love by Calvin Harris and Rihanna, scoring 33 and landing seventh out of eight on the Strictly leaderboard.
They performed the routine in the Blackpool Tower Ballroom, the first time the show has returned to the iconic venue since the pandemic.
During that show, Fleur East scored the first perfect score of this year's competition for her Couple's Choice routine with Vito Coppola to a Destiny's Child Megamix.
Earlier this season, Anton Du Beke called Kym's Charleston during Movie Week the "best dance of the series".
This isn't the first time a contestant on the series has had to miss a week due to COVID-19.
Strictly Come Dancing continues on Saturday 26th November at 7:15pm on BBC One, with the results show airing on Sunday 27th November at 6pm.