Sameer Chaudhary and his wife had come to celebrate New Year's eve at a five-star hotel in Chanakyapuri, police said.
Since it got late, they decided to book a room and stay at the hotel for the night, they added.
They checked out from the hotel on January 1 and after moving a little away from the hotel, Sameer's wife realised that her solitaire was missing, police said.
When the room where the couple had stayed was searched, there were no signs of a diamond ring, police said.
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Sameer filed a police complaint and an investigation has been taken up in the matter, they added.
Police is scanning the CCTV footage and questioning the staff members.
"In the footage obtained from the hotel, two employees can be seen going into the room after the couple have checked out. They are being interrogated," said a senior police officer.