Chelsea's Fofana undergoes knee surgery, faces extended absence

Fofana sustained ACL injury during Champions League match in October, missing World Cup.
Fofana suffered similar knee problem in December after returning from initial injury.
Fofana showed impressive form after returning in February from second injury.
Fofana had limited appearances for Chelsea last season due to injury setbacks.
Fofana underwent knee reconstruction surgery and will miss Chelsea's pre-season tour.