Communist Party of India (Marxist) general secretary Sitaram Yechury was admitted to the All India Institute of Medical Sciences (AIIMS) here on Monday after he complained of a high fever, sources said.
According to hospital sources, Yechury was admitted in the emergency department of the hospital in the evening.
However, the exact nature of his ailment was not revealed by the hospital.
A source from the CPI(M) said he had gone for a checkup, and was admitted due to pneumonia.
The source added that he was undergoing treatment and he is fine.
"There is nothing serious, he has been admitted due to pneumonia," the source said.
The CPI(M) leader had recently undergone a cataract surgery.