Sorrell was speaking at this morning's announcement of WPP's first quarter results, with the strong pound damping first-quarter revenues, which were up by 0.7% to £1.37bn.
"It's going to be very interesting to see how it shakes out," Sorrell said. "We buy about $200m of their media and that's up from about £150m last year. Google is a short-term friend and a long-term enemy and probably the shorter term just got a little bit shorter and the longer term got a bit closer as a result of the DoubleClick acquisition," he said.
The acquisition by Google of DoubleClick, news of which emerged last Friday, has been attacked by many rivals, including Microsoft, which say Google is becoming too powerful.
Brad Smith, the senior vice-president and general counsel at Microsoft Corp, said: "This acquisition raises serious competition and privacy concerns. It gives the Google/DoubleClick combination unprecedented control in the delivery of online advertising, as well as access to a huge amount of consumer information."
Sorrell said: "I think the DoubleClick acquisition clearly raises some regulatory issues which a number of media owners, publishers and competitors like Microsoft are very exercised about.
"It raises issues as to whether we are happy to let Google have our clients' data and our own data, which Google could use for its own purposes in contextual and targeted advertising."
Google has denied the charges levelled. Dennis Woodside, the managing director of Google UK, Ireland and Benelux, said: "We are talking about a competitive market. Users have a huge choice about how they search information. There are a lot of ways an advertiser can get out to market. There's nothing stopping them going to any number of online companies."
Yesterday Google reported net profits of $1bn (£500m) in the first quarter of 2007, a 69% increase from the same quarter in 2006.