Oil producer Exillon Energy's second-largest shareholder, Mikhail Gutseriyev, has approached the company to discuss a possible offer.
Hanberg Finance, owned by Russneft owner Gutseriyev, said Tuesday that it could offer not less than 300 pence ($4.93) per share in cash to buy the 85.1 percent stake in Exillon that it did not already own.
Exillon put itself on the block in mid-October after an approach from its founder, Kazakh businessman Maksat Arip, prompted additional preliminary approaches.
The company was valued at 428 million pounds ($701 million) as of the close of trading on Monday.