On Sunday, Didier Deschamps' men travel to 16th-placed Nice on 26 points from 15 games and with a one-point lead at the top of Ligue 1 after a goalless draw at home to Rennes on Wednesday.
After a lacklustre start to their season, champions Marseille are now enjoying a good run of form.
They top the standings in Ligue 1, are through to the semi-finals of the League Cup and have qualified for the Champions league last 16 for the first time in eleven years.
But the long-term absence of the young Spaniard could break that momentum.
"We could hire someone immediately or take a risk and wait until the January transfer window", Deschamps told the press.
Since his 7 million euro move from Osasuna in the summer, "Azpi" had become one of the main architects of Marseille's successes having started 12 league matches this season as well as four games in Europe.
But the 21-year-old ruptured cruciate ligaments in his left knee a week ago during Marseille's 4-0 demolition of fellow title contenders Montpellier.
According to reports, Marseille have shortlisted Rennes' Rod Fanni for his replacement.
Fanni, 28, is an experienced Ligue 1 player and received his first call-up for France in october 2008.
"He is an interesting player", sporting director Jose Anigo told the club's website. "He has the right profile, he is an international, he plays in France and he can play at different positions."
FRUSTRATION
Elsewhere second-placed Lille host Lorient on Saturday, while Brest, third on goal difference and one point shy of the top, face Paris Saint-Germain at the Parc des Princes on Sunday.
Promoted Brest are brimming with confidence after a 4-1 thrashing of RC Lens on Tuesday in which Bruno Grougi scored a double and was involved in his team's two other goals. The in-form striker helped Brest end a three-match winless streak.
PSG need to put behind them the frustration created by the draw conceded at Lyon in the dying minutes last week.
The Parisians are fourth on 23 points, two points adrift of arch-rivals Marseille, and level with Montpellier who host Lyon on Saturday.
Rennes will need to make do with a host of injured players when they entertain monaco on Saturday.
They are without defenders Kader Mangane, Onyekachi Apam and Kevin Theophile-Catherine and midfielders Alexander Tetey, Sylvain Marveaux and Fabien Lemoine.
