The world number four has not played since losing to Czech Lukas Rosol in the second round at Wimbledon in June and has been suffering from a partial tear of the patella tendon and inflammation of the left knee.
The 11-times grand slam winner was unable to defend his Olympic title in London and had to withdraw from the U.S. Open.
The Spaniard is set to join a high-profile field including Novak Djokovic and Andy Murray for the three-day Mubadala World Tennis Championship in Abu Dhabi which gets underway on Dec. 27.
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