Former prime minister Manmohan Singh is stable and his condition has improved, even as he tested negative for Covid-19, hospital sources said on Monday.

Singh (87) was admitted to the AIIMS on Sunday evening after he suffered a reaction to a new medication and developed fever.

According to the sources, Singh is stable and under observation at the Cardio-Thoracic Sciences Centre of All India Institute of Medical Sciences (AIIMS).

The sources close to him said the senior Congress leader was 'better' on Monday and did not have any fever during the day.

He, however, underwent a series of tests and some of the test results are awaited, they said.

Singh may be discharged in a day or so, the sources added. 'His sample was taken for ruling out coronavirus infection and he has tested negative for it,' a source said.

'Manmohan Singh was admitted for observation and investigation after he developed a febrile reaction to a new medication,' the sources said.

'He is being investigated to rule out other causes of fever and is being provided adequate care. He is stable and under the care of a team of doctors at the Cardio-Thoracic centre of AIIMS,' they said.

'All his parameters are fine, they said.

Singh, a senior leader of the opposition Congress, is currently a member of Rajya Sabha from Rajasthan.

He was the prime minister between 2004 and 2014.

In 2009, Singh underwent a successful coronary bypass surgery at the AIIMS.

A number of leaders expressed concern over his health and wished him a speedy recovery.