Chelsea's Senegalese center-back, Mamadou Sarr, is undergoing a medical today at Real Sociedad, where he will play on a season-long loan without a buy option, according to L'Equipe. The Basque club is a potential opponent for Levski in the Europa League, being in Pot 1 for tomorrow's draw at 2:00 PM Bulgarian time. The 20-year-old Senegalese international came through the Olympique Lyon academy and has also played for Strasbourg in Ligue 1. He is under contract with Chelsea until 2033. Sarr was loaned to Strasbourg for the first half of last season, where his consistent performances earned him the captain's armband. The defender has also played for Belgian side RWD Molenbeek, and his father is former Senegal international Pape Sarr.