The Baggies are currently three points above the relegation zone in the Premier League table with eight games left to play.
Foster believes that the club need nine more points in order to secure safety following last weekend's 2-0 defeat to Hull City.
"There are two really big games coming up," the Birmingham Mail quotes Foster as saying. "Hull was a big game, but we've got to put that behind us now and move on because Cardiff is a massive game – another six-pointer.
"Results went for us at the weekend so we're quite lucky in that sense, but we can't focus on them too much, we need to start picking points up as well."
Sunderland, Cardiff City and Fulham currently occupy the bottom three spots in the standings.