Glaverbel closed up 0.4 eur at 147.0. The main Bel 20 index meanwhile closed 17.23 points lower at 2,688.04.
Glaverbel, which is 55 pct-owned by Asahi, is unaware of the identity of the funds rumoured to be acquiring its stock, a company spokeswoman said.
Delaware-based OZ Management has declared it has acquired 5.43 pct of Glaverbel SA's capital, and is continuing to acquire them, although it is not acting in concert with a third party, the stock exchange said yesterday.
L'Echo reported that several funds, including Belgian-based ones, are also acquiring Glaverbel shares and may together hold 12 pct.
Asahi Glass is currently offering 145 eur to buy out the company, against Glaverbel's historic highs close to 150 eur.
"There are strong rumours of funds buying Glaverbel stock and that they may hold 10 pct," KBC Securities analyst Marc Leemans said.
It is not clear if they are trying to block the Asahi bid, which is dependent on it acquiring 90 pct.
It is strange that the price has been holding above the 145 bid price, he said, noting that volume has risen today from several hundred typically to over 7,000 so far.
Under Belgian takeover law, Asahi cannot offer to a second batch of shareholders a price higher than that offered to the first.
Succeeding in forcing a cancellation of the bid and a new one at enhanced terms would therefore mean all shareholders would benefit, dealers noted.
The Belgian Banking and Finance Friday postponed for two weeks the deadline for it to provide its view on the Asahi prospectus, Leemans noted.