Schwimmer fell ill on Thursday while traveling in New York with her ninth-season celebrity partner Mark Dacascos and -- while she initially hoped to recover in time for Monday night's live performance episode -- he will now perform with previously ousted professional Anna Trebunskaya, Peoplereported Monday.
"I have total faith in Anna," Schwimmer told People. "I know she and Mark will have perfect chemistry and hopefully I'll feel well enough to cheer them on backstage."
Trebunskaya -- who was eliminated during the fourth week of the competition with celebrity partner Chuck Liddell -- received a call on Friday night asking her to fill in for Schwimmer during weekend rehearsals with Dacascos, according to People.
"I was supposed to help him out and train on Saturday," Trebunskaya told People, adding Schwimmer subsequently got "really sick" -- prompting a request for her to perform with Dacascos on Monday night's performance show.
Trebunskaya said filling in for Schwimmer "has definitely been a challenge" since she's been training hard with Dacascos for two Monday night routines -- the samba and paso doble, which is this week's group routine.
"We rehearsed 12 hours Saturday and again Sunday," Trebunskaya told People.
Schwimmer said she's "thrilled" to have someone as accomplished as Trebunskaya fill her shoes and is hopeful her illness won't sideline her for more than Monday's performance episode.
"Remember to vote so Mark and I can dance next week!" Schwimmer told People.