UEFA has warned FC Sion that they face being kicked out of the Europa League after flouting a one-year transfer ban imposed upon them this summer.
The Swiss club's ban was originally imposed in 2009 when goalkeeper Essam El Hadary broke his contract with Egyptian club Al-Ahly to join them, but it only took effect in January after a lengthy appeals process.
Sion eliminated Celtic in the play-off round on Thursday but used players signed this year and UEFA is ready to throw them out of the competition and reinstate the Scottish club.
"It [Sion] signed players and then played these players in clear violation of the ban," UEFA President Michel Platini said.
The news came just hours before the draw for the Europa League group stages on Friday.
"Sion will be in the draw but on the condition that there is this protest which will be looked at by the (UEFA) disciplinary body," UEFA general secretary Gianni Infantino confirmed.
Sion landed a tough draw with Atletico Madrid, Udinese and Rennes.