Manchester City midfielder Samir Nasri could be banned for up to four years by the World Anti-Doping

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."

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."

WADA rules state that there is a 50 millilitre limit for active athletes.

The agency'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."

WADA is awaiting the AEPSAD report on this matter before making a ruling.

"As with all anti-doping matters, we will be monitoring the work conducted by the applicable anti-doping organisation," spokesman Ben Nichols told The Independent.

"It is important that information is provided to and gathered by the investigating anti-doping organisation as quickly as possible and in as much detail as possible, because the longer the period between the incident and the investigation, the greater the risk that certain evidence may no longer exist.

"Anti-doping organisations are required to come to a decision efficiently and without undue delay as to whether the proceedings should be brought against the athlete or other person."

Violation of article 2.2 of WADA's code could result in a punishment of up to four years, Nichols told the newspaper.

Sevilla have not commented on Nasri's case because the investigation is ongoing, although El Pais reported that the Spanish club was unaware the player had undergone a treatment.

Nasri, who has made 10 league starts for Sevilla, has not been suspended while the investigation is carried out and played in the Copa del Rey defeat at Real Madrid on Wednesday.