Lord Black had been discussing a partial sell-off of Hollinger International, the firm that owned the Daily Telegraph, it has emerged.
Lord Black is pondering his next move
Documents filed with US regulators show that Lord Black discussed the sale of a "substantial" stake in Hollinger earlier this month.
Those negotiations were taking place while Hollinger was selling the Telegraph to the Barclay Brothers.
The news comes amid speculation that Lord Black may try to block that sale.
The potential buyer was US investment firm Cerberus Capital Management, the Reuters news agency reported.
Earlier this week, the Barclays - owners of the Ritz Hotel and the Littlewoods shopping catalogue - agreed to buy the Daily and Sunday Telegraphs, as well as the Spectator magazine, for £665m.
Lord Black, who holds a minority stake in Hollinger International via his holding company, Hollinger Inc, questioned the financial terms of the deal, and said it should be put to a vote by Hollinger shareholders.
Lord Black had tried to sell his Hollinger stake direct to the Barclays late last year, but the deal was successfully challenged in court by other Hollinger investors.
The documents filed with the Securities and Exchange Commission, the US financial markets regulator, make it clear that Cerberus has not yet come forward with a firm offer to buy part of Hollinger.
Separately, Hollinger International said it had sold its share of the building that houses the Chicago-Sun Times newspaper to property developer Donald Trump.
The deal, worth $73m, gives Mr Trump full control of a project to build a new 90-storey skyscraper comprising flats, hotel accommodation and shops on the site of the Chicago-Sun Times building.