The former Ready Steady Cook star was on Union Row in Aberdeen at around 1am yesterday when he was assaulted.
Mr Nairn, who became Scotland’s youngest chef to win a Michelin star in 1991, had been at an event at his nearby Cook School premises before the incident.
He suffered bruising to his face and was taken to Aberdeen Royal Infirmary.
Mr Nairn, of Stirling, said it was only due to a friend intervening that his attackers fled.
He tweeted: “I’m a bit peeved but fine.”
Pc Alan Gordon said: “With festive celebrations ongoing Aberdeen city centre was busy last night with people out socialising.
“I would ask that if anyone saw this incident to contact us. In particular, we believe two males wearing black jackets and jeans may have information that could assist us with our inquiries.
“Anyone with information about this incident is asked to contact Police Scotland on 101 quoting reference 169 of 22 December.”
Speaking to a newspaper, the 58-year-old said: “As we were walking back two guys came past us, two guys in their 20s, something was said, I’ve no idea what, we carried on walking and the next thing one of the guys hit me – I didn’t see it coming.
“I was on the deck. I was out. I think I hit my head and passed-out for a few seconds.
“My good looks may have been slightly dented. It didn’t break my nose. It’s just a very deep cut.
“The first responder police and ambulance service and the guys at the hospital were excellent.”
After Mr Nairn tweeted as picture of his bruised face, messages of support flooded in including some from fellow chefs.
Mark Greenaway wrote: “That’s terrible. I hope you’re OK chef and getting medical care. Don’t just brush off head injuries. I hope you catch the scumbags.”
His followers on Twitter were equally appalled. Erikka Askeland said: “Oh how awful, Nick! Hope you recover over Xmas and the miscreants who did this are brought to book!”
Katie Pathiaki wrote: “Oh my god, I hope you’re okay –not just physically but mentally too. What an awful thing to happen at any time, but especially before Christmas. Wishing you a speedy recovery. X”
And Douglas Gillespie said: “That is atrocious chef. Take care and hope you feel better really soon.
“What a dreadful thing to happen to some like you who does so much for others.”
Later Mr Nairn told a newspaper: “I’ve been in some of the dodgiest cities in the world and nothing like this has ever happened to me before.
“We weren’t in some dark alley, we were on a main thoroughfare.
“If Union Street is a bit of a battleground at busy times then maybe the police should put more officers on the street.”
He said the incident would not force him to cancel any appointments and his family Christmas will still go ahead.
But he added: “I’ll be getting taxis everywhere I go from now on.”