Newcastle are one of two Premier League sides - along with newly-promoted Burnley - yet to register a victory this season as manager Alan Pardew continues to find himself under pressure.
The St James' Park club have picked up just one victory from their last 15 top-flight outings, a record that Shearer insists has to end on Saturday.
"The most important [game] is the next one, they have to win at home against Leicester," he told reporters.
"They've had a poor start; they've had a poor sort of seven or eight months, right back to January hasn't been good enough.
"[Pardew] knows that, the fans know that, but the players are the ones who can do something about it and they've got to do that and do it pretty soon."
Pardew's side sit 18th in the standings.