TalkTalk's parent company has announced plans to renegotiate the price it is paying to acquire Tiscali.
The Carphone Warehouse is looking to amend its £236 million offer for the company after it was revealed the broadband provider has around 160,000 less customers than previously claimed.
As the deal was made on a per-customer basis, the Times has suggested the value of the takeover may drop by up to £25 million.
Charles Dunstone, Chief Executive of Carphone Warehouse, told the newspaper that figures relating to the deal were "effectively overstated".
He added: "When we looked in the cupboard there was less than we had been led to believe."
Earlier this week, Carphone Warehouse revealed that TalkTalk enjoyed a "stronger than expected" performance during the second quarter of this year.
In a trading update, it revealed that the UK broadband provider added 77,000 net new customers over the period analysed.