One agency's head of TV said: "I understand that Reckitt Benckiser has severely reduced its investment with Channel 4.
"I imagine this is because the brand is looking to reduce costs and I would have thought a cheap way to buy airtime is to purchase broad audiences such as adults and housewives."
He added: "Channel 4 is the most inappropriate channel to target those audiences through."
Reckitt Benckiser spent £88m on TV over the past 12 months, with £14m going to Channel 4, according to Nielsen Media Research figures.
John Overend, joint managing director of OPera, buying agency for Reckitt Benckiser, said: "All of our clients have different briefs and we are happy with all our negotiations for 2008. We have fulfilled our clients' briefs."
A spokesperson for Channel 4 said: "We have done all our deals for 2008 and have built whatever the situation was into our plans."
Richard Oliver, head of investment at Universal McCann, said he was not surprised by the move.
He added: "The brand has grown over the past five years and put a big strain on Channel 4 to deliver efficiencies. It doesn't have the big programmes such as Coronation Street that deliver adults and housewives efficiently."
One broadcaster's sales head thought the advertiser wanted cheaper impacts and ITV wasn't necessarily the natural choice. He said: "The way Reckitt's budget works, we don't know where all of the spare money will have gone yet as it will trickle out throughout the year."