The man from Portland, Oregon and employed by a local company, was working outside of the Starkist Samoa cannery, in Pago Pago Harbour.
The acting Chief Medical Officer of the LBJ Hospital, Dr Akapusi Ledua told KHJ News the man had a significant number of deep bites on his left leg and suffered significant blood loss.
He was operated on for over four hours, and is now a stable condition.
Arrangements are underway to evacuate him for further continuing care, likely back in Portland, Oregon.
People who have fished or taken jet ski or boat rides in Pago Pago Harbour have reported seeing a shark in the vicinity of Starkist.