The K-pop superstar was headlining the 2017 SBS Gayo Daejun festival on Christmas Day when she collapsed.
Her spokesperson said in a statement that her hectic schedule was to blame for her medical problems.
“It seems that Heize’s extremely busy schedule may have taken a toll on her health,” they said.
“She had previously been diagnosed with pharyngitis, or a sore throat, and it is thought that she will now be operated on to help the worsening symptoms.”
They continued: “Based on her diagnosis at the hospital, it has been decided that she will undergo surgery.
“For now, her progress must be observed, and it appears that she will be unable to move forward with her plans and scheduled activities for the immediate future.”
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Heize, real name Jang Da-hye, was performing at the end of year concert for the Seoul Broadcasting System.
Her illness is another blow to K-pop fans following the tragic suicide of popular star Kim Jong-hyun.
The singer of Korean boyband SHINee died on Monday 18 December after tragically taking his own life.
The four remaining band members have cancelled their work schedules following the news, and bowed their heads as they arrived at the funeral to pay their final respects.
Crying fans lined the streets as they paid tribute to the late star, following his shock death.
A Korean funeral usually lasts three days, with the first two spent preparing the body and public mourning, followed by burial or cremation on the third day.