Prosecutors will drop sexual assault charges against former International Monetary Fund chief Dominique Strauss-Kahn at his next court appearance in two weeks, or earlier, because of doubts about the credibility of the alleged victim, the New York Post said on Tuesday.

The newspaper quoted an unnamed top investigator in the case who said the eventual dismissal of the charges was "a certainty".

"We all know this case is not sustainable," The New York Post quoted its source as saying.

"Her credibility is so bad now, we know we cannot sustain a case with her," the source told the newspaper, referring to the Guinean hotel maid who accused Strauss-Kahn of trying to rape her in a luxury hotel in Manhattan.

Strauss-Kahn, 62, was arrested on May 14 at New York's JFK Airport and subsequently resigned as managing director of the IMF.

But revelations that the accuser had lied about being raped in Guinea in a US asylum request and changed details of her story about what she did after the incident in Strauss-Kahn's hotel suite have undermined her credibility and left prosecutors struggling to make a case.

A judge released Strauss-Kahn from house arrest and lifted strict bail conditions on Friday, although serious charges including sexual assault and attempted rape remain in place against the man once seen a top French presidential contender.

"She is not to be believed in anything that comes out of her mouth - which is a shame, because now we may never know what happened in that hotel room," said the source quoted by The New York Post.

The newspaper said its source was at the center of the investigation and spoke only on the condition of anonymity.