"Atalanta can confirm that Isak Hien today underwent surgery to repair the proximal tendon of the semimembranosus muscle in the back of his left thigh," the club wrote in a statement.
The surgery was performed in Turku, Finland, by a specialist in tendon surgery.
"The player will begin his rehabilitation programme immediately," Atalanta wrote.
Hien was substituted in the first half against Japan and had to leave the World Cup.
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