"The patient is an 80-year-old man who has lived and ate chicken in mainland China," RTHK said.
The man is now residing at the city's Tuen Mun Hospital. No details were given on his condition.
On Monday the city admitted a 36-year-old Indonesian helper with a history of travelling to the mainland city of Shenzhen was infected with the virus.
"She has a history of travelling to Shenzhen, buying a chicken, slaughtering and eating the chicken," Hong Kong health minister Ko Wing-man said then.
Officials have since said it will quarantine 17 people who had been in close contact with the Indonesian patient.
The city has also stepped up border health checks with extra health officials deployed to carry out random temperature checks at entry points to the city, which already have thermal imaging systems.
Hong Kong is especially alert to the spread of viruses after an outbreak of Severe Acute Respiratory Syndrome (SARS) swept through the city in 2003, killing 299 people and infecting around 1,800.
Hong Kong's health department was unable to confirm the new H7N9 case when contacted by AFP.