Houllier said: "Michael was just a couple of games away from being on his very best form again. It is such a shame that he has been injured again. He is frustrated be he's a strong lad and will recover.
"We will miss him. Just as Manchester United would miss van Nistelrooy and Arsenal would miss Henry. Only Chelsea have a lot of options.
"These things happen to players who are lively and always on the go. It has not been a good season for us in terms of injury. Maybe we have been spared in recent seasons, but it shows the importance of having a good squad.
"It is a tough time but as a manager you know you are going to have that sometimes and we have to get on with."