La Blaugrana had eight representatives in Luis de la Fuente's Spain squad as La Roja clinched the 2026 FIFA World Cup title last month.
Pau Cubarsi, Dani Olmo, Pedri and Lamine Yamal all played a key role and are among the players not due to report back for preseason training until August 12th.
New signing Anthony Gordon and France star Jules Kounde are also scheduled back on that day after reaching the semi-finals in North America.
However, as per reports from Mundo Deportivo, Gordon is keen to get a head start on life in Catalonia and has been training alone at the Ciutat Esportiva Joan Gamper, alongside Joan Garcia and Eric Garcia.
Flick will make a late call over whether he can involve any of his returning stars in Barca's final preseason clashes against Basel and Al Ahly in the coming days.
The Catalan giants kick off their Spanish league title defence away at Elche on August 23rd.