Trinity Mirror has been subject to an "enforcement order" by UK regulators, restricting it from accessing information about the Daily Express and Daily Star newspapers.
The owner of the Mirror stable agreed a £127m deal to buy Express owner Northern & Shell earlier this year. The takeover is currently subject to two regulatory investigations by Britain's broadcasting and competition watchdogs.
Ofcom and the Competition and Markets Authority opened probes on Tuesday at the request of culture secretary Matt Hancock. While work is carried out Trinity Mirror is only able to access "limited financial information for Express and Star".
Today, Trinity Mirror said sales had fallen nine per cent in the first four months of the year. Print revenues dipped 11 per cent and circulation sales were seven per cent lower.
Trinity Mirror "estimated" Express and Star revenues fell five per cent on a like-for-like basis. While print sales fell eight per cent, the group's digital revenue surged 40 per cent.
"I am pleased with the actions we have taken to protect print profitability whilst continuing to build our digital revenue," said Trinity Mirror chief executive Simon Fox.
"Our tight management of the business, the completion of the acquisition of the UK publishing assets of Express and Star, and appropriate investment in building our digital business make me confident that 2018 will be another year of progress."
Read more: Trinity Mirror buys Express owner for £127m