The vice-president of Gremio, Odorico Roman, claims Barcelona target Arthur will not be allowed to leave the club for less than his release clause of €50million.
Earlier this month, the midfielder was forced to deny reports he has agreed to join the LaLiga leaders after he was photographed with representatives of the Catalan club.
Arthur is a rising star and helped Gremio to the 2017 Copa Libertadores title, shortly after which he was snapped in Barca colours during a meeting with sporting director Robert Fernandez.
Roman says Barcelona will have fierce competition for Arthur's signature from fellow European giants Real Madrid, Chelsea and Inter.
"Gremio renewed Arthur's contract for three years, his clause is €50million and we do not plan to sell for less," Roman told Cope.
"If Barca come with an offer of 25 or 30 million euros, Arthur will not go for that money.
"From the press, we know that there is also interest from Chelsea, Inter and Real Madrid."