Kumar, 93, was rushed to the Lilavati hospital in suburban Bandra on Wednesday morning.
"He had swelling in his right leg and we wanted to get it investigated properly. So we took him to the hospital.
Also, he undergoes routine check up every few months and that is being done as well," the actor's wife Saira Banu told PTI.
"He is doing fine...There is nothing to worry. His blood test was done this morning," she said.
Kumar also took to Twitter today to assure fans about his health along with his pictures from the hospital.
"Feeling much better now. Was admitted to Lilavati hospital for routine checkup. Your prayers are with me," he wrote.
In another post he said his personal physicians are taking care of him.
"A wonderful team of doctors here along with my personal physicians Dr S Ghokale, Dr Nitin Ghokale and Dr R Sharma.
Health is wealth said somebody. Mein aap sabhi ka mashkoor hoon ki aapne hamesha apni dua'on mein mujhe yaad rakha ( I am grateful to you that you have always remembered me in your prayers)."
The veteran actor will be turning 94 on December 11 and Saira hopes he is back home by then.
"I hope and pray that he will be at home on his birthday," she said.
Kumar was admitted to Lilavati hospital in April this year following respiratory problems.
During his six-decade long career the legendary actor, whose real name is Mohammad Yusuf Khan, has acted in many superhit films like "Madhumati", "Devdas", "Mughal-e-Azam", "Ganga Jamuna", "Ram Aur Shyam" and "Karma".
He was last seen on-screen in the film "Qila" in 1998.
Kumar was honoured with the Dadasaheb Phalke award in 1994 and the Padma Vibhushan in 2015.