Murat Kurnaz was "sexually stimulated in a helpless position" by "three women in lacy bras and panties" at the controversial prison in Cuba, lawyer Bernhard Docke told the online version of Spiegel magazine in Berlin on Thursday.
"He was tied up and chained up by scantily clad women who told him he was attractive and said they could have fun together," the lawyer added.
One of the women sat on his lap while another rubbed her breasts against him. When he managed to push one of the women away, he was beaten by guards, Docke said.
"It is not hard to imagine how disturbing this is for someone who has spent three years in solitary confinement," Docke added, saying his client had strict religious beliefs.
The Washington Post said on Thursday that a Pentagon investigation had confirmed accounts from Muslim detainees at Guantanamo that female interrogators had paraded in front of them and in numerous cases, red dye simulating menstrual blood was smeared on them.
The report, which has not been released to the public, reflects a military investigation led by Vice Admiral Albert Church III of US detention and interrogation practices worldwide, an unnamed Defence Department official told the paper.
The official said two female interrogators had been reprimanded for using sexually suggestive tactics on prisoners.