Mulayam Singh was admitted at Medanta Medicity hospital in Sec-38, Gurgaon.
A.K. Dubey, medical superintendent of the hospital, declined to comment. "I am not authorised to comment," Dubey told IANS.
Sources said Mulayam Singh was brought to the hospital at 1.30 a.m. on Saturday. He is being treated for swine flu under a team led by Sushila, a doctor.
Swine flu has claimed many lives across the country including Uttar Pradesh.