I have a player who got injured for the 3rd time this season, after being recovered with packs..And what's more surprising is, he's the best one in my team. When I message the customer service, they tell me the player is "injury proned" just like alexander pato, just like in real football lol. No need to say anything more..
Using too many red packs to keep healing players, seems to make the player even more prone to injury. I very rarely use packs to heal players. Just let them recover in their own time.