Former Chelsea boss Avram Grant believes Diego Costa 's sale to Atletico Madrid has hurt the club. Grant says Chelsea should've fought harder to keep the Spain striker. "One should not have let Diego Costa 's departure be so simple and thought that everything will resolve," he told Sky Sports. "Top teams today release no one. There are new times and there is a lot of money in the sport. It affects you. If you pick out Diego Costa you can see one of the reasons that Chelsea has been weak this year." On Antonio Conte , Grant added: "Had I been in his shoes, I would really like to stay a year to show everyone that I'm keeping my weight."