The trial of Drew Peterson has been suspended until Tuesday to let the ill juror recuperate, the Chicago Tribune reported.
"I don't want anyone else to get sick. So were going to recess today and give that individual an opportunity to get better," said Judge Edward Bermila.
Before the trial went to recess, jurors heard testimony from Anna Marie Doman, the sister of Kathleen Savio, whom Peterson is accused of killing in 2004.
Doman testified that Peterson threatened to kill her sister a few weeks before her death.
"I asked her what was wrong, and she said Drew had told her he was going to kill her, she wasn't going to make it to the [divorce settlement] trial and she wasn't going to get his pension or the kids," Doman said.
She however did not come forward with this information until 2007, which defense lawyers questioned her about.
"You sat on this information [the alleged threat] until 2007, correct?" lawyer Joe Lopez asked.
"They wouldn't listen," she said about her alleged attempts to tell police about the threat. "I called and they wouldn't listen. They would just say it was under investigation."
Peterson was charged with Savio's murder in May 2009. He has pleaded not guilty.