If Garnacho comes to Chelsea, it will be good for Chelsea, but if this player does not come to Chelsea, then this player will not have a bad effect on the performance of this club. Chelsea is a fairly balanced team at the moment, so they will not want to mess up their balance position by taking this player into the team. If Chelsea takes this star from Manchester United, then I think they will not include this star in the starting eleven, but first the manager will observe his games well in the practice session and Chelsea will decide to include him in the starting eleven depending on how well he can contribute to the club in a particular position. Since the negotiations are going on now and there may be a compromise between Chelsea and Manchester United.  
If Chelsea are not willing to pay a higher price and Manchester United are not willing to compromise on their position, the deal may not be completed and the player may remain at Manchester United.