The 25-year-old sustained ligament damage during Saturday's 3-1 win over Middlesbrough at The Den.
"Liam suffered significant ankle ligament damage and he will be out for a minimum of eight weeks," said physio Bobby Bacic.
Better news for the Lions was the return to action of midfielder Tamika Mkandawire, who got 90 minutes under his belt in an under-21 game against Barnet on Tuesday.
Mkandawire, who has been out for almost a year with a knee injury, told the club's website: "I'm glad to come through unscathed. The plan was to play 60 minutes and take it from there, but I played the full game and I'm glad I did. It's a massive step for me."
Skipper Paul Robinson, yet to feature this season after a hernia op, also played in the 3-1 win against the Bees.
- Tamika Mkandawire