Industry onlookers say buying sprees are likely to stop as groups' plunging share prices mean they will be unable to find sufficient funding. Also, owners of takeover targets are likely be nervous of any offer involving payment in shares.
In the meantime, agency networks are bracing themselves for significant drops in adspend as consumer confidence threatens to collapse.
Maurice Levy, the chairman of Publicis Groupe, warned: "Our clients are looking at their stock price and know they have to be cautious."
This week, share prices in the media sector mirrored the volatility of the market. WPP's stock price slipped by 26.5p before rallying at 587p. M&C Saatchi shares fell to 107.5p from 140p in mid-November.
"What's happening is bound to limit what we do in terms of expansion," David Kershaw, the M&C Saatchi chief executive, explained.
Bob Willott, the editor of Marketing Services Financial Intelligence, said the smaller marketing services companies were likely to suffer more as fund managers switched to what they considered less risky investments.