Majstorovic raptured a cruciate ligament during a training session ahead of Sweden’s friendly in Croatia on Wednesday.
The 34-year-old will undergo surgery in the next few days.
A statement on Celtic’s official website read: “Celtic’s medical team will be in close liaison with the Swedish FA medical team to ensure that Daniel receives the best of care.
“Unfortunately he will be out long-term. Everyone at Celtic wishes Daniel a speedy recovery from injury.”
“I will do all I can to get back as quickly as possible,” Majstorovic told the Swedish FA’s official website.
“I still feel I have a lot to offer on the football pitch and I won’t give up on my career just for this.
“At the same time I fully understand how serious this is and the work I need to put in to get back.”
