 On 30 August 2017, the 19-year-old Retsos was sold to Bayer Leverkusen for a fee of £15.75 million.The Bundesliga outfit believe they have signed themselves a future star, with the teenager having already broken records in his career.The 19-year-old centre-back has signed a five-year deal with the Bundesliga outfit after Leverkusen beat off competition from Ligue 1 sides Stade Rennes and Lyon for his signature.