Gavi was showing a decent performance before getting injured. So his absence would be felt of course. By the way I have read interesting news about him recently. It was saying that FIFA were going to pay Barcelona 20k euros per day during Gavi's injury. Is this really true? If it is then I must admit that I'm hearing about such thing for the first time in my life. 
It's nothing new anymore for FIFA to treat Barcelona is a special team, many matches in the past the referees were supporting Barcelona by not make a fair judgement, the decision is always pro to Barcelona. Not to mention robbery of Ballon d'Ors. So it's not surprising for FIFA to help Barcelona in terms financial.
Things like this should not be done by FIFA, if they do the same thing with other clubs then it is legitimate, but if there is special treatment to only one club, it seems like it is a very stupid thing to do by a big federation like them.
Actually, there are many cases that harm other parties and only benefit Barcelona, but they seem to have never been touched by heavy sanctions against them. Things like this will get a jealousy for other clubs, and it will be very bad for football.