When players are this bold about moving to a rival club of a team who deems them surplus to requirements, they most times play out their best if signed to the new team just to make a big statement to the former club. Chelsea I think should capitalize on this and sign Alejandro Garnacho before the end of the season. I strongly believe he wants to tell the management of Manchester United that he's the quality player they actually need and there's no other way to do it than to put out great performances on the pitch.
Chelsea will be playing in UCL and also be competing to win the English Premier League title next season so having a talented winger like Garnacho I think will be a very good move for the club.