CBI sources said Nagar has been served the notice to appear the agency for questioning on Friday.
"We have initiated investigations on the basis of a first information report," a CBI spokesperson had said after registration of case against Nagar.
Accused of beating up, raping and threatening the victim, the 53-year-old former Dairy, Khadi and Rural Industries Minister had to resign days after the case was registered against him at Sodala police station in Rajasthan.
Since Nagar was a sitting MLA, the case was transferred to the state Crime Branch-Crime Investigation Department.
The CB-CID recorded the victim's statement and sent her clothes for forensic examination.
The matter was later handed over to CBI for a probe.