In a note to investors, the bank forecast that the group's operating margin would come in at 14.8%, short of its 15% target but higher than last year's 14%.
CSFB said, "We lowered our margin forecast given the difficulty in paring back expenses as revenues decline rapidly. We feel the company's stated goal could prove difficult to realise this year."
Most of the savings the group can achieve are expected to come from its acquisition of Young & Rubicam.
Last month WPP, which also owns Ogilvy & Mather and J Walter Thompson, reported a 4% rise in revenues for the first five months of the year. At the time, it said that the company expects profitability to grow to 15.5% in 2002.
The company's share price was down 3.6% this morning in early trading to 693p from last night's close of 719p. The group's shares have fallen 18% this year.