The Dutch international was omitted from the squad for Wednesday's Group A game at Bayer 04 Leverkusen after tearing his calf. And the club admitted today that he could also miss the home Matchday 8 fixture against Newcastle United FC on 10 December.
"Although the injury isn't that serious, it is in a problem area," said the club's medical staff. "He should be available for the Newcastle game, but we cannot be certain."
De Boer will, however, be sidelined for the forthcoming league matches against Real Sociedad and Rayo Vallecano. Reserve-team player Oleguer Presses was called up to replace the 32-year-old in the squad for the BayArena clash.
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