Sengar has already been arrested by the CBI in connection with the alleged rape of 17-year-old-girl in Uttar Pradesh's Unnao district. He was sent to seven-day CBI custody by a court here on Saturday.
The name of the detained woman is Shashi Singh, who allegedly took the victim to Sengar on the day of crime.
The CBI has registered three cases against Sengar in regard to the crime he allegedly committed last year.
An FIR was lodged against the BJP MLA on Thursday under sections 363 (kidnapping), 366 (abduction of woman), 376 (rape), 506 (criminal intimidation) of the Indian Penal Code (IPC) and Protection of Children from Sexual Offences (POCSO) Act, and the case was handed over to the CBI.
The victim's family had also alleged that the accused MLA's brother, Atul Singh Sengar, along with his companions also raped the girl and thrashed the victim's father on April 3 for refusing to withdraw the FIR over the same. The father of the Unnao rape victim later died in judicial custody.
Atul Singh and five other accused were sent to jail on Thursday.
A medical superintendent and a casualty officer at UP's Unnao district hospital were also suspended on Friday in connection with the said case.