There has been speculation surrounding the Denmark international's future this summer, with a number of clubs thought to have expressed an interest in signing him from Barcelona.
Christensen featured as a second-half substitute in Barcelona's La Liga opener against Valencia last weekend, but he missed Friday's training session, sparking injury fears ahead of Saturday's clash with Athletic Bilbao.
According to journalist Alex Pintanel, the defender is now facing two months out of action due to a long-standing problem with his Achilles tendon.
Christensen will allegedly undergo a treatment plan which is expected to last for at least two months, with the 28-year-old therefore set to miss a number of matches for the Catalan giants.
Christensen has an issue with his Achilles tendon
The Dane struggled with an ankle issue towards the end of last season, and Barcelona allegedly believe that a period of treatment now will allow him to address his injury concerns.
Barcelona could potentially be forced into the transfer market for a new defender before the deadline, as Mikayil Faye is closing in on a switch to Rennes, while Clement Lenglet is believed to be joining Atletico Madrid on loan.
Ronald Araujo, meanwhile, will be on the sidelines until the latter stages of his year due to a hamstring operation which he underwent in the middle of July.
Pau Cubarsi and Inigo Martinez started the middle of the defence against Valencia last weekend, but there are some concerns over the latter's own injury situation.
Which other players are also unavailable for Barcelona?
Barcelona are also currently missing Ansu Fati, Frenkie de Jong and Gavi, but Pedri made his return as a second-half substitute in the 2-1 success over Valencia last time out.
Fati could potentially leave Barcelona on loan before the end of the transfer window, but De Jong will stay despite recent claims that there could be a late exit.
De Jong's ankle issue which he suffered in March is still keeping him on the sidelines, and it is currently unclear when the Netherlands international could return to action.
Gavi, meanwhile, has been absent since the end of last year due to the ACL injury that he suffered while representing Spain.
Barcelona will be bidding to make it back-to-back wins at the start of the new La Liga campaign when they welcome Athletic Bilbao on Saturday evening.