The former Bordeaux defender appears set for a lengthy lay-off after sustaining a serious knee injury in the weekend's Ligue 1 match
The 33-year-old stopper featured from the start in Saturday's 1-1 draw against Nice, but was replaced after just seven minutes after picking up an injury.
Marseille have announced that a scan undergone on Sunday has shown 'a severe knee injury with an anterior cruciate ligament tear'.
It is still unknown how long Diawara will be out for, as the club's medical staff will continue to examine the player over the next 48 hours.
The news comes as a huge blow to Marseille ahead of the Champions League tie against Bayern Munich as the Senegal international has been a key player in Didier Deschamps' side, with 33 competitive appearances to date in 2011-12.