The England striker has been suffering from calf and now groin problems this season.
Agbonlahor missed the first three games of the campaign because of a calf injury and had to be substituted after half an hour of last week's Carling Cup win over Blackburn with a similar setback.
Houllier admitted: "My concern is Gabby because he again has felt his groin.
"We will have to investigate a bit more. The calf problem has gone now. Now it's gone up his body. I hope it doesn't get much higher."
Houllier has received encouraging news regarding central defender Richard Dunne and striker John Carew.
The duo are making good progress after knee and back problems respectively and should be in contention for the trip to White Hart Lane.
Caretaker boss Kevin MacDonald had indicated Carew was struggling to play back-to-back matches because of his back complaint before he was replaced by Houllier.
Dunne suffered his setback in the clash at Stoke just over two weeks ago.
But Houllier admits the form of Carlos Cuellar as his replacement has given him a welcome selection headache.
He said: "That sort of headache I can take. A bad headache is when you've not got enough players.
"Carlos looked strong and solid and reminded me of Jamie Carragher. He goes for everything in the air and is brave."