Dembele was sent off in the closing minutes of Barca's 4-0 LaLiga win over Sevilla after a confrontation with referee Antonio Miguel Mateu Lahoz, who had just given debutant Ronald Araujo a red card for a foul on Javier Hernandez.
Barcelona's initial appeal against Dembele's red card was dismissed and he was ruled out of the club's next two league matches.
With the France forward seemingly set to miss the Clasico against Real Madrid, which had been scheduled for 26 October, Barca then attempted to have his ban halved.
Its efforts proved in vain but Dembele will now be available for the first LaLiga Clasico of the season, with the fixture having been postponed because safety concerns amid the ongoing political tensions and protests in Catalonia.
Instead, the former Borussia Dortmund star will miss Saturday's match against Eibar and the meeting with Real Valladolid a week on Wednesday (AEDT).
The Camp Nou Clasico appears set to be played on 19 December (AEDT) after both Barca and Madrid proposed the date on Saturday (AEDT).
Dembele has made three league appearances for Barca this season, scoring once, against Sevilla.