Police say the 26-year-old was in the water at Port Macquarie about 6.15pm (AEDT) on Thursday, when he felt something hit his right hand.
When the man discovered cuts to his right hand and blood on his leg he took himself to Port Macquarie Hospital, where doctors told him his wounds were consistent with a shark bite.
"He did not see a shark and was unaware at the time that he could have been bitten by one," NSW police said in a statement.
The man was treated for puncture wounds to his hand and a laceration to his leg, but was expected to be released.
Police said the northern end of Shelley Beach, where the suspected attack happened, was isolated and not widely used.
Officers could not find anyone else in the water when they visited the beach.
An expert is now set to visit Port Macquarie to try to identify the species of shark involved.
The suspected attack came just five days after Port Macquarie teenager Zac Young was killed by a shark while body-boarding further up the NSW coast.
The 19-year-old was in the ocean with three friends at Riecks Point, near Coffs Harbour, on Saturday when a shark bit off his legs.
He died shortly after his friends managed to drag him to shore.
