NAPLES, Italy — Napoli hopes to have Arkadiusz Milik back in training in January after the in-form Poland forward was injured on World Cup duty.

Milik posted a photograph on his Twitter account Monday from the hospital in Rome after undergoing surgery on his left knee.

The 22-year-old Milik damaged ligaments during Poland’s 3-2 win over Denmark in Warsaw on Saturday.

Napoli team physician Alfonso De Nicola says he is “optimistic” about when the player signed to replace Gonzalo Higuain can return.

De Nicola tells the club’s radio station “it will be shorter than what we declare, let’s say three months, 3-1/2 months.”

Milik has scored three goals for Napoli in the Champions League and four in Serie A since joining from Ajax after Higuain moved to Juventus.