Eliota Fuimaono-Sapolu could face disciplinary action for his foul-mouthed Twitter rant following Samoa's 17-10 defeat to Wales.
The Gloucester centre accused the International Rugby Board of "unfair treatment" after Samoa were forced to play for the second time in four days while Wales had a week off.
Fuimaono-Sapolu accused the IRB of exploitation and compared Samoa's treatment to slavery, the holocaust and apartheid. An IRB spokesman said: "It is very disappointing."
Fuimaono-Sapolu could be disciplined if he is found to have broken the World Cup code of conduct, which contains social media guidelines. There is also an onus placed on each nation to enforce those guidelines under the participation agreement.
Samoa coach Titimaea Tafua insisted after the game with Wales that his side's four-day turnaround was "not an excuse", but Fuimaono-Sapolu was enraged and tweeted: "IRB, Stop exploiting my people. Please, all we ask, is fairness. If they get a week, give us a week. Simple. £equity £justice."
He later added: "Ok, it's obvious the IRB are unjust. Wales get 7 days, we get 3. Unfair treatment, like slavery, like the holocaust, like apartheid. **** U.
"Give Wales 3 days off, and give Samoa a week!! We would kill them!!!"
The fixture schedule is more onerous on the Tier Two nations because World Cup organisers want to timetable the leading countries in prime-time slots to maximise commercial revenue.
Sixty per cent of the IRB's World Cup revenue comes from broadcast contracts and that money is then reinvested in the game, to set up high-performance centres in countries like Samoa and Argentina.
It is understood the only way the IRB can solve the current fixture issue would be to reduce the tournament to 16 teams, which would undermine the very point of trying to grow the game.