It seems that Alex picked up an injury at the end of the Arsenal game and now looks set to miss 3 weeks of action. Before you press the panic button I thought I should lay down a few words of caution.
1. Alex has been sensational value this season and is third among all defenders I track in aPPMS. With the other two being El Mohamady (who is overly reliant on attacking points) and Salcido (who has only played 3 games) I would not bet against Alex leading the lot when the season is done.
2. Three weeks sounds bad but it could result in him missing just one EPL start - at Villa in GW8. This isn't a great defensive fixture anyway and so if your squad works out well you may not even lose that much. They also play Wolves at home (a very good defensive fixture) in 18 days so if Alex missed that one it would be a blow.
3. Alex has seen his price rise by 0.1m already this week after his big week so only a massive fire sale will cause his value to fall.
My advice: stick with him. Concentrate on improving your bench around him to plug the gap for one or two gameweeks and get ready to welcome him back soon as Chelsea's defensive fixtures are great until GW15.