Real sit 11 points behind Barca, with a game in hand, having lost two and drawn four of their opening 15 games of the season.
Salgado, who played for Real between 1999 and 2009, does not believe that Saturday's encounter will have long-standing implications for the title race, however, insisting that both teams will lose games between now and the end of the season.
"Both teams must win the Clásico, because it's the game of the year for the fans. You always have to try to win it," he told Goal .
"The Clásico won't decide La Liga title. There's 8 real points between them [11 but with one game less for Real], and whatever happens the tournament will be still alive. There's still more than half of the tournament to go. Just some days ago we were talking about 10 points between them, and now there's an option of being just 5 points far away.
"There's still many games to play until the end of La Liga. There's still time to be up & down. And that's also discounting the Champions League, which always demands a lot to the squads, physically and mentally.
"Both teams are going to lose games. That's why the Clásico won't decide everything. But obviously, for Real Madrid it would be important to reduce the distance to just five points for the mood."
Barca prepared for the encounter with a 4-0 win over Deportivo, while Real have been away at the Club World Cup, beating Gremio 1-0 in the final.