Northern Foods' shares closed up 4% after it confirmed that Harry Ramsden owner Ranjit Boparan had asked to see its books, raising speculation that he is planning a £300m takeover bid.
Mr Boparan's company, Boparan Holdings, said there was "no certainty" at this stage that it would make a formal bid for Northern.
If any bid from Mr Boparan is made, it may end Northern's plans to merge with Irish firm Greencore.
That deal was announced last month.
Since that time, Mr Boparan has increased his shareholding in Northern Foods from less than 3% to 6.6%.
Northern Foods and Greencore plan to create a new firm called Essenta, with both sets of shareholders due to vote on the proposed deal on 31 January.
In a statement, Northern Foods reiterated its support for the merger, saying it offered "substantial benefits for its shareholders" and recommending that shareholders vote in favour of the deal next month.
Boparan Holdings also owns the FishWorks restaurant chain, as well as chicken processor Two Sisters Food Group, which is one of Tesco's largest poultry suppliers.
Greencore is the UK's biggest sandwich maker.
Northern Foods owns Goodfella's Pizza and Fox's biscuits, and is the UK's largest maker of Christmas puddings.