Issa Laye Lucas Jean Diop (born 9 January 1997) is a French professional footballer who plays as a centre-back for Premier League side West Ham United.
Diop was born in Toulouse and played youth football for Balma SC before moving to Toulouse FC in 2006. He began training with the first team in September 2015, and signed a professional contract in November. He was part of an influx of young players to the squad that included Alban Lafont, Zinédine Machach, Alexis Blin and Yann Bodiger.
He made his Ligue 1 debut, aged 18, on 28 November 2015 against Nice, playing the full game alongside fellow debutant Lafont. He scored his first goal in his second appearance on 2 December 2015, contributing to his club's 3–0 win away to fellow relegation strugglers Troyes. He made 21 appearances in his first season, helping the club to eight clean sheets. He was sent off twice during a season in which the club only avoided relegation with a win on the final day.