According to Goal, Flick confirmed that Yamal can play in Barcelona's La Liga match against Valencia.

According to Spanish media reports, Yamal missed Barcelona's group training on Saturday, leading to doubts over whether he could take part in tomorrow's fourth-round match.
Yamal stayed in the indoor gym for training, while other available teammates trained under Flick's guidance.
When asked about Yamal's situation at the press conference, Flick said: "He came out to train a little later, but he is ready to play tomorrow's match."
Regarding the reason for Yamal's individual training, Flick said according to AS: "He had a slight knock (injury), so it was better for him to train at a lower intensity, but he can definitely play tomorrow."
With a win, Barcelona will have the chance to take sole possession of the La Liga lead with 12 points. Real Madrid remain on 9 points after suffering their first defeat of the season, a 0-1 loss to Real Betis.