The 37-year-old Polish international will miss the highly anticipated El Clasico against Real Madrid on October 26.
Lewandowski sustained the hamstring injury during international duty with Poland in a World Cup qualifier against Lithuania, in which he played the full 90 minutes and found the back of the net.
However, subsequent assessments revealed a tear in the biceps femoris of his left leg - a setback that now sidelines him for several key fixtures across both domestic and European competitions.
The timing of the injury couldn't be worse for manager Hansi Flick, who must now prepare for one of the season's most decisive fixtures without his first-choice striker. Lewandowski is expected to miss LaLiga clashes against Girona, Elche, and Celta Vigo, in addition to Champions League group matches versus Olympiacos and Club Brugge.
While Barcelona's statement was vague, only noting that the striker's return "will depend on how the injury evolves," Spanish media reports estimate a recovery period of four to six weeks.
Lewandowski's absence adds to an already congested treatment room at Camp Nou. Fellow attackers Dani Olmo and Gavi are also unavailable, with Olmo nursing a calf strain and Gavi facing a longer-term layoff. Goalkeepers Marc-Andre ter Stegen and Joan García are also sidelined, with the former recovering from back surgery.
However, there are some silver linings. Promising youngsters Lamine Yamal and Fermín Lopez have returned to full training, and Brazilian winger Raphinha is pushing to be match-fit in time for El Clasico after missing the last three matches due to a thigh problem.
Hansi Flick has urged Barcelona to maintain their momentum as they travel to Sevilla to face Real Betis today aiming for a fifth straight La Liga win, and the German has used the build-up to highlight the growing influence of Eric Garcia.
Joan Laporta has reignited the tension between Barcelona and Real Madrid after declaring that Los Blancos "represent power", while insisting Barcelona stand for "freedom".
Real Madrid's hard-fought victory over Athletic Bilbao came with another unwelcome injury scare, but the Spanish champions remain hopeful that Eduardo Camavinga will still feature against Celta Vigo on Sunday.
Raphinha has firmly closed the door on any exit from FC Barcelona for the foreseeable future after putting pen to paper on a new deal that keeps him at the club until June 2028.
