Prakash was allegedly assaulted by AAP MLAs during a meeting at Chief Minister Arvind Kejriwal's residence February 19 night.
Jain has not been coming to the Chief Minister's Office (CMO) since the incident, the sources said.
The Delhi Police had last week told a court that during interrogation, Jain disclosed that AAP MLAs Prakash Jarwal and Amanatullah Khan surrounded the chief secretary and saw them assaulting him at Kejriwal's residence.
The alleged assault on Prakash took place in the presence of Kejriwal and his deputy Manish Sisodia.
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"The chief minister's advisor has gone on a week-long medical leave. He has not been attending the office since the alleged assault on the chief secretary," sources told PTI.
Jain was appointed advisor to chief minister soon after he had retired as the CEO of the Delhi Urban Shelter Improvement Board (DUSIB) in August last year. The board is chaired by Kejriwal.
The joint forum of the Delhi government employees has demanded action against Kejriwal and Sisodia in connection with the case of assault on chief secretary.
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