Dembele reacted to a decision made by referee Mateu Lahoz, and the 22-year-old was given his marching orders when he called the official very bad.
Dembélés dismissal left the Catalan giants sweating over his potential participation in the top of the table clash with Madrid after the international break, and the wingers two-match suspension was reported by Què Thi Jugues on Wednesday afternoon.
The former Borussia Dortmund man is set to miss Barças trip to Eibar in two weeks time, and will then be unavailable for El Clásico which will take place at Camp Nou.
Barcelona protested Dembélés sending off, with Lionel Messi claiming that the Frenchman struggles to form sentences in Spanish and his intentions were lost in translation, as he is unable to express himself clearly.
The youngsters suspension has been upheld however, and Los Culés will have to make do without their pacy forward for the biggest game of their season thus far.
The La Liga champions have made a solid start to the new campaign, sitting second in the table, and victory over Los Merengues could see Messis men overtake their arch rivals.
The Argentine star bagged his first goal of the season against Sevilla on Sunday, curling in a trademark free-kick to round off the scoring in an impressive performance by the home side.
Dembélé also scored in the demolition of Julen Lopeteguis side, but his petulance at the end of the match has cost Ernesto Valverde dearly.
The France international had already picked up a yellow card earlier in the game against Los Hispalenses, but his outburst towards the referee earned him a straight red card, meaning a two-game suspension was inevitable for the Barça star.