Microsoft's head of online operations, Kevin Johnson, has taken a new job at Juniper Networks, according to the Wall Street Journal.

Juniper spokeswoman Sarah Sorensen would not confirm the report, saying the company does not comment on "rumours and speculation." Microsoft has not responded to a request for comment.

Johnson was head of Microsoft's platforms and services division, and as such was also responsible for the development and marketing of Microsoft's Windows products.

He has been instrumental in Microsoft's attempt to acquire all or part of search rival Yahoo. Microsoft's online services business reported a $488 million (£244 million) loss in operating income for the fourth quarter, more than double the $210 million operating loss the division saw last year.

Johnson has been with Microsoft since 1992. "In some ways, he has had a career trajectory somewhat like [CEO] Steve Ballmer's own. He was definitely on the short list of people who would be a potential CEO replacement," said Rob Helm, an analyst with Directions on Microsoft. Helm was also unable to confirm Johnson's departure.