Christensen, 29, made his first start since September in Tuesday's Copa del Rey tie against Guadalajara, scoring the first goal in the 2-0 win.
However, Barça say he suffered an "unfortunate twist of the knee" this weekend, ruling him out of Sunday's LaLiga game against Villarreal and for the foreseeable future.
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"After tests carried out on the player, a conservative course of treatment has been chosen," the club said in a short statement. "The player's recovery time will depend on his development."
It's the latest in a string of injuries Christensen, who is out of contract next summer, has suffered over the last two years.
The Danish centre-back was limited to just six appearances in all competitions last season, mainly due to an Achilles problem, while a calf injury sidelined him earlier in the current campaign.
Prior to that, he had made 74 appearances in his first two years at the club after joining from Chelsea on a free transfer, playing a key role as Barça won LaLiga in 2022-23. Christensen's injury leaves Barça short in the middle of defence, with Ronald Araújo also currently absent after being granted a mental health break.
Pau Cubarsí and Gerard Martín, a converted full-back, are currently the preferred centre-back pairing, but Jules Koundé and Eric García are also options to play there if required.
The shortage could see Barça turn to the transfer market in January. A source told ESPN earlier this month that, providing Araújo returns to action in 2026, they would not be active mid-season, but Christensen's injury could change that stance.
