French champions Monaco have warned suitors of in-demand teenager Kylian Mbappe that they will report any clubs who contact the striker without their consent to governing body Fifa.
Mbappe, who netted 26 times in a sensational breakout campaign last season, is believed to have interested a host of Europe's leading clubs including Real Madrid, Barcelona, Arsenal, Chelsea, Manchester City and Manchester United this summer.
Monaco condemned unnamed teams who they say have approached the 18-year-old in an illegal manner by failing to seek their permission first.
"AS Monaco regretfully notice that important European football clubs made contact with Kylian Mbappe and his entourage without our authorisation," the club said in a statement.
"AS Monaco want to remind these clubs that such actions are contrary to article 211 of the administrative regulations of the French Ligue de Football Professionnel and to the article 18.3 of Fifa's regulation of the status and the transfer of players.
"To put an end to this unacceptable situation, AS Monaco consider asking the French Ligue de Professionel and Fifa to commit disciplinary procedures against the offending clubs."
Members of Monaco's young squad have been much sought after in this summer's transfer window, following their role in Monaco's first Ligue 1 title in 17 years and a run to the Champions League semi-finals.
Yet after selling midfielders Bernado Silva and Tiemoue Bakayoko to Manchester City and Chelsea respectively for a combined £85m, Monaco have taken an increasingly hard-line stance.
City have had a £44.5m offer for full-back Benjamin Mendy turned down, while Arsenal have failed with bids of up to £45m for midfielder Thomas Lemar and United have been frustrated in their attempts to sign the versatile Fabinho.