Maybe the coach is just trying to make Garnacho understand that he is not indispensable from the team so that he can put in more effort to become better because once a player starts thinking that they are untouchable in a team, the chance of their performance to reduces increases then. Some of these players need a wake up call and if he doesn't move in this window before it expires it will be a wake up call for him to really put in more effort to impress the new coach so as to maintain the first team selection.
Some of the players that Manchester United have do not show good attitudes because sometimes they are too selfish and they are not able to work well together with the team. Players like this do need to be given a little pressure so that they can change and in the future the competition in the Europa League will increase where they will face much tougher opponents so Manchester United must improve their quality if they want to stay in the title race. Players must be able to be at their best because the Europa League provides a way for Manchester United to qualify for the Champions League if they succeed in winning.