The fullback had hoped of seeing action against Champions League opponents Dynamo Kyiv.
Firpo was expecting Koeman to rest Jordi Alba and give him a chance. But the Dutchman again went with the veteran left-back.
Sport says Firpo was left stunned and disheartened. While Koeman has rotated his squad since the season kicked off, Firpo has been left on the sidelines.
A move away in January is now expected for Firpo, who has seen just 31 minutes under Koeman this term.