Lionel Messi will be out for up to eight weeks after suffering knee ligament damage in Barcelona's 2-1 win over Las Palmas on Saturday, the Catalan giants confirmed.
"Tests have confirmed that Leo Messi suffered a torn internal collateral knee ligament. The estimated time out will be seven to eight weeks," Barcelona said in a statement.
Messi, 28, looks set to be sidelined for at least eight Barca games, as well as Argentina's first four 2018 World Cup qualifiers, including a meeting a home to Brazil on November 13.
Moreover, he is now a huge doubt for the first El Clasico of the season away to Real Madrid on November 21.
Barca face Sevilla, Rayo Vallecano, Eibar, Getafe and Villarreal in La Liga before visiting the Bernabeu.
The European champions host Bayer Leverkusen in the Champions League on Tuesday and will also have to do without Messi for back-to-back games against BATE Borisov.
Messi clashed with Las Palmas defender Pedro Bigas as he tried to turn the ball home inside the area and suffered a blow to his left knee in the process.
He briefly returned to the field after receiving treatment, but was clearly unable to run freely before he was replaced by Munir El Haddadi.
Video images then emerged of Messi limping heavily he left hospital after undergoing tests.
It is the first serious injury Messi has suffered since a hamstring injury kept him out for the final two months of 2013.