Arthur and his agent Andre Curry reportedly met Barcelona representatives in Porto Alegre this week and a photo of the 21-year-old wearing a Blaugrana shirt was leaked on the internet, reports Xinhua news agency.
"He is our player. Barcelona are creating problems with Gremio by trying to influence the kid," Gremio's legal advisor Nestor Hein told Estudio Gaucha.
"We'll put together a formal complaint to submit to FIFA accusing Barcelona of manipulation as soon as we have full confirmation about the way they acted."
FIFA forbids clubs from approaching contracted players without the consent of their employers.
Gremio football director Odorico Roman accused Barcelona of acting "improperly", adding that the Catalan club did not seek permission for talks with the player.
"We have not been approached by Barcelona and we are not negotiating with them," Roman told a press conference.
"If Barcelona want him, there is a buyout clause but my position is that they will not be able to negotiate."
A Barcelona spokesperson could not immediately be reached for comment on Saturday.
Arthur has been a revelation for Gremio this year and last week helped the Porto Alegre outfit to their third Copa Libertadores title, South American football's top club trophy.
The former Goias youth-team player was rewarded for his impressive 2017 form by being called up to Brazil's national squad for their last 2018 World Cup qualifiers against Bolivia and Chile in October.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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