The Ranbaxy stock ended the day at Rs 560.75, up 6.53 per cent from the previous day's close of Rs 526.4.
Some banks have taken a position in Ranbaxy in the last one month in anticipation of a strategic stake sale by the promoters of the company, the Singh family.
Merchant banking sources said Da-Ichi was in advanced negotiations to buy into Ranbaxy.
Earlier, Takeda, which is Japan's biggest pharmaceutical company, was said to be in similar talks with the Indian company. When contacted, it did not decline that such talks were going on. Merrill Lynch is Ranbaxy's advisor on the deal.
Ranbaxy officials shrugged it off as market speculation, though the company has called a board meeting tomorrow.
Ranbaxy Managing Director Malvinder Mohan Singh is scheduled to address the media in the afternoon in New Delhi.
The Singh family owns around 35 per cent in Ranbaxy. The family also owns a majority stake in Fortis Hospitals and Religare Securities.
Ranbaxy share prices, which were lying low till recent months, saw a sharp rise after Solrex Pharma, a company wholly owned by Ranbaxy, started acquiring significant shares in Chennai based Orchid Pharmaceuticals.
The talks of a possible stake dilution to a Japanese firm triggered further rise in its share prices during the last one month.
