Real Sociedad coach Philippe Montanier is bracing his in-form side for what he anticipates will be Athletic Bilbao's best performance of the season when they take on their struggling Basque rivals.
Athletic have endured a tough campaign following their impressive cup exploits of last season, and they head into the derby stuck only six points above the Primera Division relegation places following successive defeats to Espanyol and Malaga.
That Espanyol loss was particularly hard to stomach as it saw Athletic humbled 4-0 in front of their own fans - the club's joint heaviest defeat at San Mames in over a decade.
However, Montanier, whose side are sixth heading into the match and 11 points better off than their rivals, is not expecting things to be so comfortable for his men tomorrow.
The Frenchman said: "We really want to make our fans happy because we know it's a special game for them, but I know full well that we can't expect a great result if we don't have a great game.
"Athletic are a very strong team and their league placing doesn't reflect their real level."
He added: "The derby is a special game which is always somewhat crazy. The league standings can't be used to judge the chances of the two teams.
"Athletic are a dangerous side. We know that in this game we are going to find the best Athletic of the season."
While Athletic have slipped back towards the drop zone in recent weeks, Sociedad have stormed up the standings on the back of a hugely impressive run.
They have lost just once in their last 14 league matches - a 4-3 defeat to Real Madrid at the Bernabeu - while picking up seven wins, including triumphs over Barcelona, Valencia, Malaga and Sevilla.
However, Sociedad have a poor recent record at San Mames, where they have picked up only one point since 2001, and Athletic will be desperate to continue that run tomorrow and boost their survival hopes.
Athletic defender Andoni Iraola insists the three points are the most crucial aspect of the clash.
"Clearly, the derby is a special game, with many factors, but above all this is the situation we find ourselves in the table, which means getting the points is the important thing," he said.
"We're coming off two painful defeats, we are in a bad situation and there aren't too many games left. We need to get up the table as soon as possible."