As per official statement by barcelona here
“Tests carried out on Monday morning on the first team player Gavi have shown that he has a complete tear of the anterior cruciate ligament in his right knee and an associated injury to the lateral meniscus. The player will have surgery in the coming days after which a new medical update will be released. Gavi was injured on international duty for Spain in the final game of the team's European Championship qualifying group against Georgia. The Barca midfielder was forced off after just 26 minutes of the encounter.”
https://www.goal.com/en/lists/worst-case-injury-scenario-gavi-barcelona-confirm-midfielder-tore-acl-spain-surgery-knee/Barcelona was not giving a club how long needed by him to recover from his injury but the club said that if he is likely going out for months. Probably till the end of season (my prediction). It sounds bad for gavi but not for barcelona caused by there are also some players are starting to recover from their injured. Gavi will be missing so many matches. Probably he will comeback next season to play in the club again. this is a bad news for gavi. Unexpected injury that happened to him.
It is not a good news for Gavi and Barcelona and hopefully he will recover well from the injury and will return as strong as he used to be. I really hope that Gavi will use his time for recovery to think of his playing style. Many times, he played too dangerously for himself and if he wants his career won't be shortened by his dangerous playing style, he must change it. A smart player must know how to protect his body to avoid unnecessary physical clashes with opponent players that potentially cause serious injuries which can terminate his career immediately.
With this type of injury, if Gavi has to go through a medical surgery, he will need many months to come back and this season will be nearly ended for him.