The 26-year-old Spaniard, who has averaged 8.6 points and 2.1 rebounds in 31 regular season games, had already missed 12 games due to a lower back strain.
His injury flared up again during a game against the Dallas Mavericks on Monday and he was advised to have surgery following evaluation and diagnostic testing.
A date for his surgery has yet to be scheduled, casting some doubt over whether he will be fit to represent his country at the Olympics Games in London starting on July 27.
Fernandez won a silver medal with the Spanish team at the 2008 Beijing Olympics.
