Madrid
The club said Ramos did not say how long the veteran defender will be sidelined.
Players who undergo this type of surgery usually need about six weeks to fully recover.
Ramos is not likely to play Atalanta in the round of 16 of the Champions League.
The 34-year-old Ramos had been playing through pain recently and ultimately decided on surgery to be fully fit for the final part of the season.
His last game was on Jan. 14 in the Spanish Super Cup semifinal loss to Athletic Bilbao.
Among other players injured in the Madrid squad are Eden Hazard, Dani Carvajal and Federico Valverde.
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