Samir Nasri 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.
The Spanish Agency for Health Protection in Sport (AEPSAD), which handles doping issues, said on Wednesday it was launching an investigation.
The French playmaker is currently on loan to Spanish side Sevilla from Manchester City.
AEPSAD said on its official Twitter feed: "AEPSAD has initiated the appropriate steps to clarify what treatment was received by the player Samir Nasri."
According to the Drip Doctors clinic, Nasri received its "Immunity IV Drip."
The clinic stated that the treatment involves one litre of hydration and is designed to "combat superbugs and common viruses."
Drip Doctors posted a message and photograph of Nasri alongside its co-founder Jamila Sozahdah on its Twitter feed following the treatment.
- Drip Doctors (@DripDoctors) December 27, 2016
However World Anti-Doping Agency rules state that there is a 50 millilitre limit for active athletes.
WADA's prohibited list includes "intravenous infusions and/or injections of more than 50ml per six-hour period except for those legitimately received in the course of hospital admissions, surgical procedures or clinical investigations."
Nasri is due to return to Spain this week after spending part of the La Liga winter break in the United States.
Drip Doctors refused to comment when contacted by Press Association Sport on Wednesday.
Manchester City referred questions about the situation to Sevilla.
A spokesman for the Spanish club said there was no information beyond what had been reported in the media after news of Nasri's treatment emerged on Tuesday evening.
The World Anti-Doping Agency (WADA) and the Spanish authorities had been alerted to the claim about the clinic visit by a Twitter post from Richard Ings, the former head of anti-doping at the Association of Tennis Professionals (ATP).
Nasri will be able to play for Sevilla while an investigation takes place, with Enrique Gomez Bastida, the director of AEPSAD, saying no sanctions could be put in place until all the facts were known.
In an interview on Spanish radio network Cadena SER, Bastida added: "It is necessary to know in what frame and in what situations it [the IV drip] occurred.
"We will verify the facts to know where we are. You have to be careful with the rumours. In the Nasri case there is no sanctioning procedure at the moment, so there could be no interim injunction."