Marc Cucurella reportedly asked to leave Chelsea for Real Madrid due to personal reasons.
The Spaniard has been a key player for the Blues, and he has been almost ever-present in the left-back position in recent years.
However, he has now chosen to pursue a new challenge with Madrid, who have reportedly paid 60 million euros for his services.
Cucurella has already secured a formal move to Los Blancos and journalist Ben Jacobs reports that he has joined for private reasons.
Chelsea also believe they have secured a good fee for the Spaniard's exit and will now start the search for a quality replacement.
Newcastle United's Lewis Hall has been linked with a reunion with the Blues, but they have yet to make a formal offer for him.
Arsenal's Myles Lewis-Skelly is another name on the club's radar, but the Gunners may not entertain his departure this summer.
The Blues are looking at other options too. A final decision will be made after discussing with incoming manager Xabi Alonso.