Gavi is just 19th years old with starting his career and having injury like this is surely frustrated with rest of the season is already ended mean things can go from bad to worse for this wonder kid, but it's all about game we can't prevent these from happening, but it's surely needed to settle things before joining again because few players having injuries throughout their career even few lost their bright careers as well.
ACL injury is surely serious problem and Barcelona is surely feeling heat with this as well because as all soccer fans know these injuries can bring big holes in players career because it's never been easy to handle this all, but we can hope best for the Gavi as he will recover, and we will have him in game in coming years for long time.
Gavi is a young player and in theory, he still has a long career ahead but will his career last long or will it be short, it will depends on many things. Injuries are what no player want to have and sometimes they can not avoid injuries. However, a smart player will try to adapt his own playing style to reduce risk of injuries as much as possible.
Arjen Robben is a good example that a sensitive player with injuries can change himself to be stronger physically and change his playing style to avoid injuries and expand his career longer. Gavi is a player with very bad playing style as he does not proactively avoid dangerous physical fightings and it's what Gavi must spend time to think deeply with his current injury and a long time for recovery progress.