Senior advocate Anjana Prakash said this to the Supreme Court during the hearing of Singh's plea seeking judicial review of the rejection of his mercy plea by the President.
"I was sexually abused in Tihar jail. I was forced to have sexual intercourse with co-accused 31-year-old Akshay. I was also severely beaten up many times.
"All these statements were given by me but these were not placed before the President," Prakash claimed in her submission before the court.
A bench headed by Justice R. Banumathi was hearing Mukesh's plea.
Levelling serious accusations against the Tihar Jail authorities, Mukesh's lawyer added that her 32-year-old client was forced to have sex in front of other prisoners.
Mukesh and five other men, including a juvenile, had brutally gang raped and assaulted a Delhi girl on a moving bus leading to her death in over a month after the incident on December 16, 2012.
Contending that her client has been sentenced to death, Anjana Prakash asked the court "but was he sentenced to be raped?"
She also contended before the court that several supervening circumstances, which included his illegal solitary confinement, were ignored when the mercy petition was rejected by the President.
The court will pronounce it's verdict on Wednesday.
( With inputs from IANS )