Fuimaono-Sapolu posted a string of messages on Twitter, criticising the World Cup fixture scheduling after Samoa were given just three days off before their game against Wales in Hamilton last Sunday.
He accused the IRB of exploitation and compared Samoa's treatment to slavery, the holocaust and apartheid.
World Cup organisers have now issued a statement after they met with Samoa's team management in Auckland today, revealing they had accepted an official apology.
"Rugby World Cup Limited officials met with the Samoa team management today to discuss comments made by a member of the Samoa squad via the public social media network Twitter," read the statement.
"While RWCL believes the nature of the comments to be inappropriate and has warned the Samoa Rugby Union regarding future social media conduct, RWCL has accepted an official apology and is satisfied with the proactive measures that the Union has outlined to RWCL to address the matter.
"There will be no further action, and RWCL considers the matter to be closed."
Fuimaono-Sapolu, 30, had written on Twitter: "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 like Samoa 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.
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