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I don't think Enzo Maresca dropped Robert Sanchez as Chelsea's first choice goalkeeper without reason. It's likely due to squad rotation and Sanchez's slightly dip in form. As a result, Maresca has opted to give Filip Jorgensen a chance, which is a reasonable decision to maintain competition and freshen up the squad.
If Sanchez decides to leave the club, I don't think Chelsea will miss him. They already have solid goalkeeping options, and in the event of his departure,they could recall kepa arrizabalaga from his loan spell at Bournemouth. Chelsea has young goalkeeping prospects, Djordje Petrovic, who could step up if needed.
Enzo Maresca has given Robert Sanchez the chance to prove his quality, but he has failed to live up to the coach's expectations. The decision taken by Enzo Maresca is very reasonable and previously Hansi Flick had done the same thing to Inaki Pena, now he is more trusting the main goalkeeper position to Szczesny.
Chelsea certainly won't be short of players if Robert Sanchez chooses to leave the club, there are still plenty of other goalkeepers who can be relied on to strengthen the team.