#1 Achraf Hakimi

The Real Madrid loanee has pretty much been a bargain of the season for Dortmund. He has been the vital part of Lucien Favre's highly-entertaining side. At just 20 years old, Hakimi has contributed outstanding 3 goals and 7 assists in all competitions, despite playing as a defender.
A versatile player, the Moroccan has played equally well as a fullback on both sides. He is a heavily attack-minded player and might be Sarri's dream choice to fill the right-back position. He has outstanding dribbling and passing capabilities. Hence, he would suit much better to Chelsea's current system than Azpilicueta.
Real Madrid have bought Alvaro Odriozola for the right-back position to compete with Dani Carvajal while Marcelo is likely to stay at the Los Blancos left-back following Zinedine Zidane's appointment. Hence, Hakimi's homecoming to Bernabeu could be highly unlikely in an ideal world but the powers at the Bernabeu rate him highly.
Still, should Madrid decide to sell, Chelsea would have the upper hand in signing the starlet due to their better financial power compared to Dortmund.