The 19th-placed Baggies are 12 points behind Graham Potter's Albion with thirteen games remaining this season.
Allardyce said: "This is one of the hardest games we're going to have this season because Brighton are one of the most productive sides in the league. The only thing that has been missing for them this season has been scoring goals.
"I am convinced they would be in the top 8 if they had a finisher, maybe even better. I have seen the quality of their performances and what they've been able to put together.
"There's been times where they haven't finished teams off this season and that's why they are sitting in the bottom half.
"I'm expecting a massively difficult game. I don't want my players to take this lightly by thinking it's going to be anything other than extremely difficult.
"It'll be a totally different game to Burnley who are well-organised and direct. Brighton play to their strengths by being flexible in their systems and playing through the lines as quickly as possible.
"It's a big game and one we cannot take lightly."