Houllier said: "I hope Stephane may be able to play again for us before the end of the season. He flew back with me to Paris and on to Geneva on Monday to see a specialist, but we already had an idea as to what the problem was.
"We decided not to play Stephane against Birmingham, but he played against Auxerre and then again in the final on Sunday.
"He played through the pain barrier which, to me, embodies the spirit and the resolve of the players here in this club.
"He didn't just pick the final - he wanted to play against Auxerre, too. There is a risk that if he doesn't have the operation now and plays on, he could damage his Achilles tendon.
"Stephane has been very good for us. He is an unsung hero in defence. His partnership with Sami Hyypia has been great.
"We'll always miss good players obviously, but we have Djimi Traore, whose best position is centre back, and we have Igor Biscan. Jamie Carragher can also play there.
"Sometimes it's a good opportunity for the other players in the squad to show what they can do."