Centre Eliota Fuimaono-Sapolu was banned for six months after last year's Rugby World Cup for a Twitter post which described Welsh referee Nigel Owens, who controlled Samoa's match against South Africa, as racist and biased.
The 23-test veteran had been censured after an earlier Twitter comment which likened Samoa's World Cup schedule to slavery, apartheid and the Holocaust.
In naming his squad for next month's Pacific Nations Cup, coach Stephan Betham said the IRB had instructed Samoa not to select Fuimaono-Sapolu.
"The International Rugby Board has ruled against Eliota playing rugby in IRB-run tournaments. It was made known in a letter," Betham told reporters.
But the IRB used its Twitter account to deny the claim.
"Eliota Sapolu not banned or ineligible for IRB or international matches," it said. "Comments by Samoa head coach disappointing and untrue."
Gloucester-based Fuimaono-Sapolu again used Twitter to dispute the IRB's statement, claiming to have evidence that Samoa was pressured not to select him.
"I have in my possession something that suggests otherwise. Maybe I disclose it all and let the people decide. Stop lying." he said.
Later on Thursday, he tweeted: "Don't put it on the coach (Betham).
"I have proof the calls were made much further up and forced on him."
Samoa's former captain Mahonri Schwalger was also left out of the squad, and said his non-selection was because he criticized Samoa Rugby Union officials after last year's Rugby World Cup, questioning their behaviour and saying the team lacked administrative and financial support.
"I knew it would cost me my international career," Schwalger said. "If it means that the (Samoa) will go forward without me then that's a sacrifice I will take."