A Central Bureau of Investigation spokesperson told : "Dagar has written an application to the agency seeking voluntary retirement from service, on personal grounds."
According to CBI officials, Dagar had applied for VRS in August-end.
However, his request has not been accepted yet by CBI Director Rishi Kumar Shukla, a CBI source said.
Dagar was part of the team that was probing Asthana, when then CBI Director Alok Verma and then Special Director were engaged in a bitter fight and levelled charges of corruption against each other.
Verma and Asthana were then both sent on forced leave by the government on October 23 in a late night decision.
However, when the government appointed senior IPS officer M. Nageshwar Rao as the acting Director of the agency on October 24 last year, he brought Dagar from the Economic Offences Wing to Anti-Corruption wing in Delhi. Dagar replaced the former investigating officers including Deputy SP, A.K. Bassi.
Dagar was given the charge to probe the alleged case of corruption against Asthana, along with DIG Tarun Gauba and Joint Director V. Murigeshan.
Dagar has, in the past, probed cases against Dera Sachcha Sauda chief Gurmeet Ram Rahim.
The CBI on October 15 last year had registered an FIR against Asthana for allegedly taking a bribe from an accused probed by him in return of ensuring relief and a clean chit in the case.
The case against Asthana was lodged after Hyderabad-based businessman Satish Babu Sana in his complaint to the CBI had alleged that he paid a bribe of Rs 2 crore to Asthana to be spared any action in an investigation linked to meat exporter Moin Qureshi. The money was paid over a 10-month period starting from December 2017.
Sana was being investigated by a SIT team headed by Asthana when he had accused him for accepting bribes.
As per Sana complaint, he had had met Manoj who claimed to have good relations with Asthana. Sana also alleged that Manoj's brother, Somesh, will help him in getting clean chit from Asthana.
However, Asthana had strongly refuted the charges placed against him as "baseless".
Sana, a close aide of Qureshi, was arrested on July 27 this year by the Enforcement Directorate in connection to a money laundering case.
( With inputs from IANS )