CHICAGO – Chicago Teachers Union President Karen Lewis, a potential challenger against Mayor Rahm Emanuel in next year’s election, is recovering after an emergency surgery Wednesday for “a serious illness.”

CTU Vice President Jesse Sharkey told the media Thursday he will take over the responsibilities of union president for the foreseeable future, but did not provide any specifics about Lewis’ condition when he spoke to reporters at the union’s downtown headquarters, the Associated Press reports.

“Karen Lewis has a serious illness,” he said. “She underwent surgery yesterday and that was successful. She is recovering well. … She’s both alert and comfortable.”

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Lewis, 61, was rushed to Northwestern Hospital Sunday night after a campaign event, but her family has kept details of her health issues under wraps. An unidentified source told NBC Lewis exhibited “stroke-like symptoms” before her operation for a “new medical issue.”

“A source insists Lewis did not suffer a stroke, and while it’s not clear what kind of emergency she had, NBC 5 was told it was not heart surgery or related to her weight loss surgery,” according to the news site.

Lewis has reportedly lost more than 100 pounds after she underwent bariatric surgery in Mexico in March. Since, the union boss has been holding a listening tour in the Windy City to gin up support for a run for mayor, though “those close to her campaign said she already has the necessary signatures to get her name on the ballot,” NBC reports.

Lewis, a former chemistry teacher at King College Prep High School who took the CTU presidency in 2010, has not officially confirmed she will enter the mayoral race.

Sharkey told reporters that Lewis, who led the city’s teachers on a self-serving strike in 2012, “will need time to recover,” but did not discuss what the recent surgery will mean for the Feb. 24 election.

“I understand that many people in this room, and many people in this city, want to know about Karen Lewis’ health status because they care about the mayoral election in this city,” Sharkey said, according to the Chicago Tribune. “I think that’s fair enough. But please be aware that’s a question that I can’t answer.”

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In a recent Tribune poll, 43 percent of respondents supported Lewis, while 39 percent favored Emanuel, who has witnessed his approval rating drop to a meager 35 percent.

Emanuel and Alderman Bob Fioretti, the only other contender for mayor, both issued statements wishing Lewis a speedy recovery.

“Karen Lewis is a passionate advocate for her beliefs and has always been willing to speak up for her view of what’s best – not only for the teachers that she represents, but also for issues critical to the future of our city,” Emanuel’s statement read. “Along with all Chicagoans, we will keep Karen and her family in our thoughts and prayers, and we hope to see her on her feet soon.”

“My thoughts and prayers are with my friend Karen and her family,” Fioretti said, according to the Tribune. “She is a fighter and I know that she will bounce back, stronger than ever. Her voice adds to the debate in Chicago and we all get better results when there is a full and spirited dialogue.

“But right now, we should all respect Karen’s privacy and give her space she needs to get better,” the statement read.