Velez Sarsfield are "angry" at Manchester City ahead of their appeal to the Court of Arbitration for Sport (CAS) over the transfer of a teenager, the Argentine club's club secretary, Bernardo Bertelloni, has told The Times.
Velez complained to FIFA last year that City broke rules preventing trafficking of minors by signing Garre after he turned 16.
The Premier League club said they could register Garre with the English Football Association and FIFA because he had an Italian passport.
FIFA respects European Union laws allowing free movement of 16- and 17-year-olds.
Bertelloni said: "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."
If Velez are successful with their appeal then City could face a transfer ban.
In May, City were given a two-year academy transfer ban, with the second year suspended, and fined £300,000 for the "tapping up" of two youngsters.
Information from the Associated Press was used in this report.