Manchester City midfielder Samir Nasri could be banned for up to four years by the World Anti-Doping Agency (WADA) if found guilty of breaching its rules.
Nasri, on a season-long loan at Sevilla, is being investigated by the Spanish Agency for Health Protection in Sport (AEPSAD).
He will have to explain the intravenous drip treatment he is said to have received at a Los Angeles clinic amid concerns he may have violated anti-doping rules.
AEPSAD, which handles doping issues, said last month on its official Twitter feed: "AEPSAD has initiated the appropriate steps to clarify what treatment was received by the player Samir Nasri.