The winger has hailed the DFB-Pokal final as a "special occasion" but has warned nothing less than a win will do on Saturday
The Bundesliga champions wrapped up the domestic title in record time with a victory over Hertha Berlin in late March, but have since struggled for consistency.
A 5-0 aggregate loss to Real Madrid ended hopes of defending their Champions League crown, while Bayern's unbeaten league record was also ruined by defeats against Augsburg and Borussia Dortmund.
Jurgen Klopp's men now stand between Pep Guardiola's side and another piece of silverware on Saturday and Ribery believes that it will be a defining game.
"If we lose in Berlin, it is not a good season," the French winger told reporters. "We need to win against Dortmund, that would make it a fantastic season.
"Playing in the DFB-Pokal final is always special. But Dortmund are in good form at the moment, we'll have to work hard."
Dortmund already ruined one chance at silverware for Guardiola's charges this season when they won the DFL-Supercup before the 2013-14 Bundesliga campaign began.
Ribery, who was a nominee for the Ballon d'Or in January for his efforts last year, may be limited to a cameo performance in Berlin after admitting he was "still feeling a little pain" from a recent back injury.
However, he is a certainty to be involved with France's squad at this summer's World Cup - barring injury - after being named in the provisional squad by Didier Deschamps on Tuesday.