MUMBAI - Bankers on the $2.5 billion share sale of India's Adani Enterprises are considering extending the sale or cutting the issue price after shares plunged on a U.S. short seller's report, said three people familiar with the deal.

Among the options the bankers are considering are to extend the Tuesday closing date for the subscription of the issue by four days, the sources told Reuters on Saturday.

Seven listed companies of the conglomerate controlled by one of the world's richest men, Gautam Adani, have lost a combined $48 billion in market value since Hindenburg Research on Tuesday flagged concerns about debt levels and the use of tax havens.

The Adani Group has called the report baseless and said it was considering taking action against Hindenburg.

Friday's 20% fall in shares of group flagship Adani Enterprises dragged it 11% below the minimum offer price of the secondary sale. On first day of retail bidding on Friday, the issue was subscribed around 1%, raising concerns over whether it would be able to proceed.

"Everyone was shocked. They did not expect such a poor response," one source said.

Adani Group did not immediately respond to a request for comment.

Adani had set a floor price of 3,112 rupees ($38.22) a share and a cap of 3,276 rupees, but Adani Enterprises closed on Friday 2,761.45 rupees.

The other option being considered is lowering the price, the sources said, with one saying it could be cut by as much as 10%.

A decision was expected on Monday, the sources said.

"Revision in price band or time extension of public issue can technically be undertaken with a newspaper advertisement and issuing an addendum," said Sumit Agrawal, managing partner at Regstreet Law Advisors and a former officer of the Indian capital markets regulator.

At the end of the first day of the share sale, investors, mostly retail, had bid for around 470,160 of the 45.5 million shares on offer, according to Indian stock exchange data.

The sale is being managed by Jefferies, India's SBI Capital Markets, and ICICI Securities among others. They did not immediately respond to requests for comment.

A fourth source said Adani management is also discussing the share sale internally to decide on next steps.

The Hindenburg report questioned how the Adani Group used entities in offshore tax havens such as Mauritius and the Caribbean islands. It said key listed Adani companies had "substantial debt", which put the entire group on a "precarious financial footing".

(Reporting by Sriram Mani and Jayshree P Upadhyay; Editing by Aditya Kalra and William Mallard)