Tata, 86, who ran Tata Sons for more than 20 years and is credited with expanding and diversifying the company, said on Monday he was undergoing routine medical investigations due to his age and related medical conditions.
A representative for Tata, one of the world's biggest conglomerates with a revenue of $165 billion in 2023-24, did not immediately respond to a request for an update on his condition on Wednesday.
The sources, one of them close to the Tata family, and both with direct knowledge of his medical condition, did not give further details on the nature of his illness.
Tata has been admitted to Mumbai's Breach Candy hospital, they said.
In a statement published on his social media profiles on Monday, Tata said he remained in good spirits and that there was no cause for concern.
Tata is not as active in the day-to-day running of the group as he used to be, but is consulted on big decisions by the Tata Sons leadership, a senior company executive told Reuters.
He is, however, involved in the running of Tata Trusts, a philanthropic organisation run by the group, of which he is chairman. Tata also serves on the international advisory boards of Mitsubishi Corporation and JP Morgan Chase, according to his profile on the Tata Sons website.
Tata became chairman of the autos to steel conglomerate in 1991 and ran the group founded by his great-grandfather more than a hundred years ago until 2012.
He founded telecommunications company Tata Teleservices TTML.NS in 1996 and took IT company Tata Consultancy Services TCS.NS public in 2004.