Houllier confirmed McGregor, 28, was watched by assistant boss Gary McAllister and goalkeeping coach Rafael Gonzalez during Rangers' Champions League defeat to Manchester United in mid-week.
"Yes we went to see him (McGregor) play," said Houllier,
"I'm very happy with Brad but I'm conscious he is 39 and I'd be silly not to look to the long term.
"Obviously, he didn't have a good game versus Blackburn but, since the start of the season, he's been spot on.
"He's got experience and I trust him. I think he's a good goalkeeper, been a good buy. Long term, we need to prepare for the future. I need to see the reserve goalkeeper (Brad Guzan) as well."
Houllier admits he is unlikely to make any major moves in the transfer window in January.
He expects several of Villa's current crop of injured players to return to action in the next few weeks including Nigel Reo-Coker and Emile Heskey.
He said: "In January, I don't think I'll make many moves because there will be many injured players coming back. I've seen Reo-Coker running and maybe in two weeks' time he'll be back.
"I am also hoping Heskey starts (training) with us on Monday or Tuesday. I also don't want to buy what we have. It's definitely in midfield where we need to buy one or two players."