Shares in paper and packaging group Smurfit Kappa had dropped over 6% by closing of trading in Dublin today amid concerns that US group International Paper could abandon a bid to buy company.
IP has a deadline of tomorrow to register its interest in Smurfit Kappa.
Smurfit Kappa has twice frustrated a bid to combine the largest listed US paper packaging firm with Europe's biggest.
It most recently rejected a raised takeover offer from IP in March, arguing it was better served pursuing its future independently.
IP, whose cash and shares offer in March valued the Irish group at €8.9 billion, said it would not make a hostile bid after being given until June 6 to make a binding offer or walk away.
Smurfit Kappa had said that it is "resolute" in its belief that the best interests of the group's stakeholders are served by pursuing its future as an independent company, operating as the European and PanAmerican leader in paper-based packaging.
"The revised proposal also fundamentally undervalues the group and remains significantly below the valuations set by recent industry transactions," it added.
IP said that it had identified at least $450m pre-tax cost savings by the end of the fourth year if the deal goes ahead.
It also reiterated its commitment to remain disciplined and adhere to its stated financial objectives.
It said that a combination of the two highly complementary businesses had "compelling strategic and financial rationale".
The bids for Smurfit Kappa came as growing consumer spending and the popularity of online shopping have boosted demand for packaging.
An acquisition would allow International Paper to significantly diversify its business beyond North America.
Smurfit, which operates in 35 countries in Europe and the Americas, recorded a slight rise in core annual profit to €1.24 billion last year after a strong fourth quarter.