The Sunday Times reported that Nippon Sheet Glass made an informal approach to a Pilkington director last month with an offer of 80 pence per share.
But the Japanese company on Monday denied it was in the process of bidding on the company.
"There is no truth to the newspaper report, although we cannot rule out future possibilities," a spokesman told Reuters news agency.
Nippon Sheet Glass is the largest shareholder in Pilkington, with a 20.4 percent stake. The offer would be a premium of a third of its closing price on Friday, of 60.5 pence per share.
Pilkington's board of directors has not discussed the offer, according to the newspaper, and CEO Stuart Chambers is believed to be unaware of the interest. But Nippon Sheet Glass has reportedly appointed advisers to draw up a deal.
The companies both make glass around the world for customers such as car and construction companies.
Pilkington recently reported a large drop in profit for the first half of its year and warned that the rest of the year was likely to be tough.
Shares of Nippon Sheet Steel rose 2.82 percent to close at 219 yen on Monday, outperforming a 1.57 percent rise in the Nikkei average as Tokyo had its first trading of 2003.