It is more a question of attitudes and professionalism. There have been several rumors, in several clubs, that JR does not train hard enough, and that he does not take care of his body as a top athlete should do. This also contributes to being injured far more frequently. However, if the problem is as big as some say, then it is a scandal of Everton's medical staff to approve the transfer.
I do not demand that JR run around telling how much he loves Everton, etc., but I expect him to behave like a professional footballer. That was what the Colombian manager expected, and at this level you can not plan and set up your game for players who are not 100 percent. Although they can hit a magic pass or two.