John Doerr

SAN FRANCISCO — Last month, John Doerr, one of America’s most celebrated venture capitalists, announced that he would step down from the board of Amazon.com, a company that he helped to finance and build. At the time, Amazon said Mr. Doerr “has decided not to stand for re-election and will focus more of his time on new ventures.”

But people with direct knowledge of the matter, who would not speak for attribution because they were not authorized to discuss it, now say Mr. Doerr’s decision was prompted by a Federal Trade Commission inquiry into the relationship between Amazon and Google, where Mr. Doerr is also a director. It was not clear whether the commission had begun a preliminary inquiry or a formal investigation, or whether it was still looking into it.