Andre Villas-Boas is hoping John Terry could return to action within a month but admitted the Chelsea captain could be out for up to six weeks.
Terry has aggravated the knee problem that has been plaguing him throughout 2012 and will miss England's friendly against Holland as well as several key matches for his club. Terry is due to undergo what is understood to be a small procedure on the right knee that has been troubling him ever since he collided with a post in last month's FA Cup clash with Portsmouth.
Villas-Boas said after the Blues' 3-1 last-16 first leg Champions League defeat to Napoli at the San Paolo stadium: "Four weeks would be excellent. We'll have to wait and see how the operation goes, and hopefully the player can return in that time frame. But normally it's six weeks."
The news is a huge blow to the club, who have not won a match or kept a clean sheet since Terry was first ruled out three weeks ago.
A six-week absence would see him miss potential Champions League and FA Cup quarter-finals as well as a host of crucial Barclays Premier League games as Chelsea struggle to secure a place in the top four.
Terry had played through the pain of what was bruising on the bone for three weeks and the club were hoping a period of rest would see him make a full recovery. But he is now set to undergo a small procedure after the Blues fly home from the match.
England caretaker manager Stuart Pearce is scheduled to name his squad for next Wednesday's friendly with Holland on Thursday.
Terry's absence relieves Pearce of the problem of having to decide whether to pick both the deposed captain and Manchester United defender Rio Ferdinand.
Terry lost the armband while he awaits trial for allegedly using a racist slur against Ferdinand's brother, QPR's Anton Ferdinand.
Terry denies any wrongdoing and the Football Association's decision to strip him of the captaincy led to Fabio Capello quitting as England boss almost two weeks ago.