Alonso has been a key component of Real's side since joining from Liverpool in 2009 and this marks a frustrating set-back for the 31-year-old after he recently recovered following groin surgery. 

The Spain international returned to training late in July and, despite missing Real's La Liga opener against Real Betis on Sunday, looked set for a swift return to Carlo Ancelotti's starting XI. 

However, the playmaker is now facing several months on the sidelines. 

Ancelotti - who took over from Jose Mourinho in June - may look to 23-year-old midfielder Asier Illarramendi to fill the void left by Alonso's absence.

Illarramendi was one of the stars of the Spain's successful UEFA European Under-21 Championship campaign in the close-season and moved to the Santiago Bernabeu from Real Sociedad for a fee of around €32million last month.