The former Liverpool boss lost a number of key midfielders to injury towards the end of last year and is hoping the signing of Bradley, who is set to arrive on loan from Borussia Monchengladbach until the end of the season, will provide cover if such an event reoccurs.
Houllier said: "At one stage in the season we had three midfielders injured at the same time. Steve Sidwell was having an operation, then in back-to-back games we lost Stiliyan Petrov and Nigel Reo-Coker so I thought 'we've got to be careful'.
"We're not in a very comfortable position in the league, we know that, and we've got to also prepare for the future.
"Michael Bradley is 23, and a very hard-working midfielder who can score goals.
"I saw him play four times out of five in the World Cup at the games."