Real Madrid are set to react after Gremio midfielder Arthur was pictured in a Barcelona shirt.
The 21-year-old has been chased by Barcelona this season after enjoying a fine season in Brazil that saw Gremio lift the 2017 Copa Libertadores, becoming the first Brazilian side since 2013 to do so.
His form saw Arthur called up to the Brazil squad for the first time for his country's final World Cup qualifiers, and although he didn't play, the midfielder is expected to become a big player for the Brazilian national team.
It's been a meteoric rise for Arthur, who only became a first-team regular with Gremio this year and is now being courted by the biggest clubs in the world.
Barcelona have moved quickly on the back of the continental success to try and secure his signing - but appear to have gotten way ahead of themselves, greatly angering Gremio.
Soon after the Libertadores victory, Barcelona Sporting director Robert Fernandez met Arthur and posed for what may prove to be a disastrous photo.
No deal has been agreed with either the club or the player, and Gremio seeing their star player in another team's shirt has convinced them that Barcelona are not the team they want to be doing business with.
Enter: Real Madrid.
Real are set to face Gremio and Arthur in the final of the Club World Cup on Saturday, and both teams are reportedly very open to the idea of discussing business, reports Marca.
Gremio will seemingly find great satisfaction in selling to Barcelona's rivals, while the draw for Real is obvious; sign a highly-rated prospect and score one over your rivals? It's the dream scenario.
The meeting between the two continental champions proves the ideal place to begin talks that would benefit both sides enormously.
Real already have some form for beating Barcelona to a Brazilian youngster, too, having paid an incredible €46m for 16-year-old Vinícius Júnior of Flamengo - a player who had made just a single senior appearance.
Barcelona, on the other hand, will be looking to do what they can to salvage a deal for a player they already had in their grasp - and unfortunately their shirt.