The 17-year-old was absent from the squad for Sunday's La Liga clash with Real Sociedad, where Barca suffered a surprise 1-0 defeat courtesy of a Sheraldo Becker goal.
Yamal had made it through the full 90 minutes of Barcelona's 5-2 Champions League triumph over Red Star Belgrade in midweek, but the club confirmed on Sunday that he had suffered a "severe contusion".
"Lamine Yamal sustained a severe contusion on Wednesday against Red Star," a medical update read. "He has undergone treatment but the discomfort isn't gone yet completely. His recovery will determine his availability."
Fermin Lopez unsuccessfully filled in on the right-hand side for Yamal in Sunday's defeat, after which Flick conceded that he did not know whether the latter would be fit to return after the international break.
Yamal to miss Spain matches after "severe" bruise?
Yamal has been called up to the Spain squad to face Denmark (November 15) and Switzerland (November 18) in the UEFA Nations League later this month, but Barcelona are hoping for him to be released from the Roja camp.
"We will miss now Lamine Yamal... I don't know if he will return after the international break. We've asked for him not to travel to national team," Flick told the media.
The 2007-born talent has gone from strength to strength yet again this season with six goals and eight assists from 16 games in all competitions, although Barcelona's run of fixtures immediately after the international break is not so daunting.
The Blaugrana's first game back comes away to Celta Vigo on November 23, three days before a Champions League showdown with Brest on November 26, and they end the month at home to Las Palmas on November 30.
The start of December sees Flick's team square up to Mallorca on the 4th and Real Betis on the 8th, before a more taxing Champions League match against 2023-24 runners-up Borussia Dortmund on December 11.
Which other players are Barcelona missing through injury?
Despite Sunday's surprise setback, Barcelona still sit six points clear of Real Madrid - who have a game in hand - at the top of the La Liga table, a feat that is even more impressive when their perennial fitness struggles are taken into account.
First-choice goalkeeper Marc-Andre ter Stegen and talented midfielder Marc Bernal are missing for the rest of the season due to serious knee injuries, while Andreas Christensen's Achilles problem is unlikely to fully heal until 2025.
Ronald Araujo (thigh), Ferran Torres (hamstring) and Eric Garcia (groin) are also in the care of the medical team, but defender Pau Cubarsi made it full the through 90 on Sunday despite suffering a nasty facial injury in the Champions League.
Nevertheless, Cubarsi has been omitted from November's Spain squad by Luis de la Fuente, who has included four Barca players in Yamal, Marc Casado, Pedri and Dani Olmo.