The 76-year-old former Defence Minister was admitted to the hospital at around 11 PM yesterday after he fell down, sources said.
A senior doctor at the hospital said today that Singh has been operated upon for head injury and he is in a critical condition in the ICU.
Singh, who had also served as External Affairs and Finance Minister, was expelled from the BJP early this year after he decided to contest the Lok Sabha polls from Barmer in Rajasthan as an Independent when the party decided to field someone else.