Financial Times publisher Pearson says the group’s full-year profits could be 40 per cent lower than last year's.
It says advertising revenues at its business titles have fallen dramatically over the last month.
And it fears half-year profits from technology publishing could be £25 million lower than expected.
Advertising revenues during September were down 40 per cent on last year at the Financial Times, while Les Echos, Expansion, FT Deutschland and The Economist also reported significant falls.
Pearson says the FT newspaper continues to increase its circulation faster than its major competitors, and to reduce its cost base.
It says losses from FT Knowledge could be £5 million sterling worse as a direct result of the impact of the terrorist attacks on the World Trade Centre, which included the New York Institute of Finance.
Pearson says sales growth in the Penguin Group has slowed.
It also says losses from its Internet enterprises should be £60 million in the second-half, down 45 per cent on the same period last year.
Ms Marjorie Scardino, Pearson's chief executive, says: "We are now expecting profits to be significantly below our original plans for the year, almost entirely because of the weakness in advertising markets and, to a lesser extent, the technology recession.
"These markets are cyclical in character and will bounce back. When they do, we will see the benefit. In the mean time, we will continue to manage our costs and our cash to minimise the impact on our financial performance."