The 94-year-old thespian was admitted to the Lilavati Hospital in suburban Bandra yesterday due to dehydration and urinary tract infection.
"He is doing much better than yesterday. But he will be in hospital today. The doctors here are taking good care of him," Kumar's wife Saira Banu told PTI.
Kumar has given memorable performances in films like "Andaz", "Aan", "Madhumati", "Devdas", "Mughal-e-Azam", "Ganga Jamuna", "Kranti", "Karma" and others.
His last film was "Qila" that released in 1998.
Known as the tragedy king of Bollywood, Kumar was honoured with the Dadasaheb Phalke Award, India's highest award in cinema, in 1994 and the Padma Vibhushan, the country's second-highest civilian award, in 2015.