Credit: Jon Kopaloff/FilmMagic

Dancing With the Stars pro Lacey Schwimmer has fallen ill and is unable to dance on tonight's episode, has confirmed.

Partnered with Iron Chef host Mark Dacascos, Schwimmer, 21, will be replaced by ousted pro Anna Trebunskaya, who got eliminated with Chuck Liddell on Oct. 14.

The dancer was stricken with the flu while traveling in New York with her partner over the weekend.

"I'm super sad to be sick today. Ugh," Schwimmer Twittered Monday. She will sit out two dances -- the samba and the paso doble, this week's group routine.

Schwimmer's fellow DWTS pro, Derek Hough, was also sidelined this season with a nasty bout of the flu virus.

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"I don't even know how to describe it," Hough told Us of his illness earlier this month, which was thought to be swine flu -- but later confirmed not to be. "It felt like horse flu! It was unbelievable. I was out."