The man known as Hammer scored a hat-trick in the Dolphins' final round 62--24 win over Canberra while playing centre before limping from the field in the second half.
Scans have revealed a grade three tear of his medial collateral ligament (MCL).
In a statement, the Dolphins said Tabuai-Fidow had been "ruled out of the upcoming Pacific Championships".
"The Hammer is expected to be ruled out for approximately eight weeks, ruling him out of the tournament," the club said.
Tabuai-Fidow will start pre-season training in November after his rehabilitation.
Before the injury, speculation had swirled over whether the 24-year-old would continue to represent Australia on the coming Ashes tour or Samoa in the Pacific Cup.
AAP was told he was leaning towards Samoa, which the Dolphins' release has subsequently confirmed.
Tabuai-Fidow has Torres Strait Islander and Samoan heritage.
The Dolphins fullback played for Samoa at the 2022 World Cup but injured an ankle in the opening match.
He then represented Australia in six Tests. He has also played 10 State of Origin games for Queensland.
"My mum is a Torres Strait Islander and my dad is Samoan so it is pretty cool to run on representing them. It is a big part of my life and to have those two cultures is special," Tabuai-Fidow said earlier this year.
"It is pretty cool how many Samoans do play in the NRL and if they do get the crew together it will be a pretty special team. I know all the boys will put their hands up to go back and play."
Samoa will kick off its Pacific Cup campaign away to New Zealand in Auckland on October 19. The Cup campaign also includes Tonga.
Papua New Guinea, Cook Islands and Fiji will contest the Pacific Bowl in Port Moresby.
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