The 32-year-old collided with Jeremy Mathieu during Real Madrid's 3-2 win against Valencia and was unable to travel home with his team-mates
The Spain international collided with Jeremy Mathieu on the hour-mark at Mestalla but soldiered on to play the rest of the match.
Alonso immediately underwent tests on the injury after the game and it has now been confirmed that he has a tear in his left eardrum.
"After medical tests on Xabi Alonso, the player has a perforated left eardrum suffered as a result of a hit he took in the match against Valencia," a club statement read.
The former Liverpool man was unable to fly back to the Spanish capital with the rest of his team-mates and will instead travel home by road.
With Madrid's action before the winter break now concluded, though, there is little chance of Carlo Ancelotti being without the 32-year-old for any matches.