Ronald Araujo struck at the death to snatch Barcelona a 2-1 win over Girona on Saturday and lift the champions top of La Liga.
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.
This latest setback resurrects an injury saga that has already seen Yamal miss four games this season.
Champions League holders Paris Saint-Germain stunned Barcelona with a 90th-minute Goncalo Ramos winner to claim a 2-1 away victory in the league stage on Wednesday.
With the new Ballon d’Or holder, PSG star Ousmane Dembele sidelined through injury, the stage is clear for his Barcelona successor to stake an early claim for next year’s crown.
Last season it was the then 17-year-old who inspired Barcelona's charge to the semi-finals of the Champions League.
Lamine Yamal returned from injury to help Barcelona beat Real Sociedad 2-1 on Sunday and move top of La Liga by one point.
The 18-year-old winger finished second behind Paris Saint-Germain attacker Dembele at the glitzy gala in Paris on Monday in the battle to be crowned the world's best player.
France forward Ousmane Dembele won the men's Ballon d'Or at a ceremony in Paris on Monday, the most prestigious individual award in football rewarding his starring role in the Paris Saint-Germain side that won the Champions League last season.
Lamine Yamal returned from injury to help Barcelona beat Real Sociedad 2-1 on Sunday and move top of La Liga by one point.
The 18-year-old winger finished second behind Paris Saint-Germain attacker Dembele at the glitzy gala in Paris on Monday in the battle to be crowned the world's best player.
France forward Ousmane Dembele won the men's Ballon d'Or at a ceremony in Paris on Monday, the most prestigious individual award in football rewarding his starring role in the Paris Saint-Germain side that won the Champions League last season.
Barcelona and Spain teenager Lamine Yamal was awarded the Kopa trophy for the world's best Under-21 player of the year for the second time in a row on Monday.
Paris Saint-Germain players are set to miss the Ballon d'Or ceremony on Monday (September 22) because of a controversial decision made by Ligue 1 officials. The Parisians' hugely successful past year is set to be celebrated in Paris when the awards showpiece takes place in the French capital.
Matchday 1 of the Champions League group-stage resumes on Thursday with another round of high-profile clashes across Europe. Manchester City’s meeting with Napoli and Newcastle’s showdown against Barcelona headline the night, while elsewhere Sporting CP host Kazakhstan’s Kairat Almaty and Frankfurt face Galatasaray. Early kick-offs see Club Brugge welcome Monaco and Copenhagen take on Bayer Leverkusen
Yamal suffered the injury while on international duty with Spain.
Barcelona coach Hansi Flick lashed out at the Spanish national team on Saturday after Lamine Yamal was ruled out of his team's La Liga clash against Valencia.
Champions Barcelona dropped their first points of the La Liga season with a 1-1 draw at Rayo Vallecano on Sunday.
Barcelona cruised to a 3-0 win at nine-man Mallorca in their opening LaLiga game of the season on Saturday as England forward Marcus Rashford made his debut off the bench.
