- Green Growth
- Your Consultant
The Brazilian has missed the Blues' last two league games, against Fulham and Sunderland but still joined up with his national side for their friendly against South American rivals Argentina in Qatar on Wednesday.
A Chelsea statement said: "Further to the Chelsea medical team's diagnosis, the Brazilian national team doctors agree that further investigation via arthroscopic surgery is required on the player's right knee.
"That will take place over the coming days.
"He is expected to be out for approximately six to eight weeks."
With fellow central defender John Terry also out with injury, the 28-year-old Alex's coninued extended absence is something Chelsea manager Carlo Ancelotti could have done without as he tries to shore up the side following their shock 3-0 loss to Sunderland.
Chelsea captain Terry is undergoing treatment to resolve a problem with a nerve in his leg which he fears could possibly rule him out for months.