Zurich - FIFA is investigating Mohamed Salah's move to Roma in a breach of contract case which could threaten Chelsea with a transfer ban.
FIFA says it "received a claim" from Italian club Fiorentina against Chelsea and Salah.
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Fiorentina challenged Chelsea's right to let the Egypt winger join Roma on a season-long loan last month. Salah spent part of last season at Fiorentina, which claims it has an agreement to extend his stay.
FIFA typically takes months to rule on contractual breach claims. If proven, sanctions include four-month bans for players and one-year bans on clubs registering new players.
In 2009, FIFA's dispute resolution chamber imposed a one-year ban on Chelsea for signing teenager Gael Kakuta from Lens.
Chelsea later agreed to a financial settlement with Lens.