The Danish centre-back suffered the injury in the 58th minute of Saturday's 3-1 win at Sevilla, in a challenge with Robbie Ure, and immediately called for the medical staff, aware that something was seriously wrong.
He was replaced by Gerard Martín and left the pitch in tears, unable to complete a match in which Raphinha scored a hat-trick, with Christensen himself setting up the Brazilian's opener.
Barcelona confirmed on Sunday, after tests, that the 30-year-old has a muscle injury in the rectus femoris of his left quadriceps, and said in a statement that he "will be out for the coming weeks" and that "his progress will determine his availability."
Hansi Flick had already said after the match that his defender would be sidelined for some time.
The setback is a familiar one. Christensen missed 32 matches for club and country in 2025-26 because of a torn cruciate ligament, plus three more with calf trouble, and the season before that cost him 37 games to an Achilles tendon problem and 16 to muscular issues. He had signed a new contract in July running to 2028 despite that history.
Christensen joined Barcelona on a free transfer from Chelsea in July 2022 and has won two La Liga titles and a Copa del Rey since, and he has 81 caps for Denmark.
Christensen had been a regular starter again this season, playing in four of Barcelona's first six matches, including successive starts against Racing Santander and Sevilla, and had begun to look like a reliable option alongside Pau Cubarsí. He had also been named in Denmark's squad for this month's Nations League games against Norway, Wales and Portugal, all of which he will now miss.
The latest injury leaves Flick needing to find a new partner for Cubarsí at centre-back while Christensen recovers, with Ronald Araújo and Eric García the most likely options in the meantime.