Valencia say Portugal forward Goncalo Guedes will be sidelined for around two months after needing surgery to his abdomen.
The Spanish club said on Friday the 22-year-old Guedes had been operated on to treat a "weakness in the abdominal wall suffered in recent weeks."
Guedes was one of Valencia's best players last season, when he scored five goals after arriving on loan from Paris Saint-Germain. Valencia bought him outright before this season for a reported €40 million.
Valencia are struggling this season and are just four points above the relegation zone before visiting Eibar on Saturday.