The Spanish international suffered a torn calf muscle last month, and his return will be in the next match, but gradually, and he will not be in the starting lineup.
In contrast, Flick confirmed that Uruguayan defender Ronald Araujo will miss the Alaves match due to a stomach virus.
Flick was excited about the return of Brazilian winger Rafinha, who played in the Catalan team's last two matches as a substitute, after being out of action for nearly two months due to a hamstring injury.
The German coach said in a press conference on the eve of the Alaves match: "I missed Rafinha. I see him as one of the most important players on our team, and he is eager to play and has the will to show how good he is."
He added: "I really appreciate what I see in training. We are focused and we have a lot of quality, and of course the players who are returning now. Pedri is back, Rafinha, and Marcus Rashford after suffering from a cold. Almost all the players are back."
Barcelona, the defending champions, are second in the Spanish league standings, one point behind their traditional rivals Real Madrid, who lead with 32 points.
