England head coach Fabio Capello has been full of praise for Walker who has made the temporary switch from Tottenham to Villa Park for the rest of the season.
The right-back spent the first part of the campaign on loan at Championship leaders QPR and has impressed since joining Villa.
Houllier said: "I share Fabio's view that Kyle is a possible England player.
"I don't think he is the finished article yet. But we have given him the chance to play in the Premier League and he has taken it well.
"I think Kyle knows that he's got a lot of areas where he can improve. But what I like about him is his attitude, that he's eager to improve to progress. He's a modern day full-back, somebody who can defend and who can also get forward."