Barcelona coach Hansi Flick said Saturday Lamine Yamal's groin injury is not simple to heal from and cast doubt over a potential return date.
The Spanish champions said Yamal would be out for two-to-three weeks in a statement on Friday, but Flick suggested the 18-year-old winger's absence could potentially be longer.
Yamal will miss World Cup qualifiers with Spain and is aiming to return before Barcelona face Real Madrid in a Clasico at the Santiago Bernabeu on October 26.
"This injury is not so easy, like a muscle (injury), we have this experience with (those), the coaches, the therapists.
"With this kind of injury, it's not easy to say now, okay, he can play in two weeks, in three weeks or four weeks, so he's able to play in the Clasico – this is not possible.
"We have to wait... we have to manage his (work) load. He will train with our recovery team, so for the next weeks he is with them, we have to go step by step and have to see how his evolution is."
Yamal suffered a groin injury while playing with Spain in September, missing four games before returning to action last week.
The teenager, recently voted the second best player in the world at the Ballon d'Or gala, played against Paris Saint-Germain in the Champions League on Wednesday, suffering a recurrence of his injury.
Flick said he had spoken to Yamal on Saturday and the winger gave him positive news.
"I spoke with him today and it's much better than before, but it's not good," said the coach, ahead of Sunday's LaLiga clash against Sevilla.
Flick criticised Spain coach Luis de la Fuente after Yamal played against Bulgaria and Turkey with pain-killing injections.
De la Fuente said Friday he expected Flick to have more "empathy" having been a national team coach himself, but the German stood by his words.
"I don't regret this, I want to protect my players," added Flick.
"It's done now, for me it's over, we have to look forwards... the important thing is that we manage this together, the clubs and the federation."