India's top court has granted businessman Subrata Roy, negotiating the sale of his assets, including hotels in London and New York, from a makeshift office in prison, another extension to seal a deal.

Roy, who heads troubled financial services group Sahara India Pariwar, now has until 30 September to sell the Grosvenor House hotel and two hotels in New York.

This is the second extension given to Roy and India's Supreme Court has warned that the latest extension will be the last, reports said.

A deal will help Roy raise funds to post a $1.7bn (£1.05bn, €1.3bn) bail in Delhi. Roy has to pay India's market regulator Sebi to get out of the Tihar jail.

The Sahara group could mortgage its trophy hotel properties rather than sell them, to raise bail money, The Economic Times reported on 5 September.

Sahara has not officially named any of the potential buyers for the hotels.

In August, a spokesman for the Sultan of Brunei dismissed reports that an investment firm affiliated with him had tabled a $2bn bid for the three Sahara hotels.

Earlier in August, Roy's steno, secretarial assistants and Sahara directors Ashok Roy Choudhary and Ravi Shankar Dubey were given access to a conference room in the prison, following a court order.

American real estate investor Madison Capital has tabled an $800m bid for Roy's US hotels – the Plaza Hotel and Dreams Downtown Hotel.

An investment arm of the Qatari royal family and an Indian pharma billionaire, Cyrus Poonawalla, have offered to buy the British property, which is located in the Mayfair area and managed by J W Marriott.

Roy has been in jail since 4 March after two group companies - Sahara Housing and Sahara Real Estate - failed to comply with the Supreme Court's order to refund $3.9bn to 30 million investors.

Roy acquired the New York hotels for close to $800m in 2012 and had purchased the Grosvenor for $725m in 2010. The acquisitions were financed through borrowings from the Bank of China.