Manchester City have been accused of tapping up an underage player and could face a transfer ban if found guilty.
The Court of Arbitration for Sport (CAS) is set to investigate Man City's signing of Argentine teenager Benjamin Garre from Velez Sarsfield last year.
Velez argue that Man City tapped up Garre when he was 15 years old, and the Argentine club complained to FIFA that the deal was in breach of its regulations in relation to signing youth players, who can only be approached after they have turned 16.
Club secretary Bernardo Bertelloni is quoted by ESPN as saying: "We're angry because Manchester City came after our player, we said no and they took him anyway. That's not good behaviour between two clubs.
"They made us a written offer [before his 16th birthday]. We rejected it, in writing, saying we weren't prepared to transfer him because it was prohibited by FIFA. The rules are clear, you can't transfer a player before he turns 16 under any circumstances.
"In response, City told us they were going to ask FIFA for an exception. The player left here when he was 15. He left here a couple of days before his 16th birthday, he spent a few days in Germany and he entered England one day after his 16th birthday.
"Man City argued that there is an exception in the FIFA rules that said that because he has a European passport he could be transferred. But the FIFA rule does not say that, it says he can move only within the EU, between EU clubs."
In May, Man City were given a two-year academy transfer ban, with the second year suspended, and fined £300,000 for the alleged tapping up of two youngsters.