Issa Laye Lucas Jean Diop is a French professional footballer who plays as a centre-back for Premier League club Fulham.

In association football, a substitute is a player who is brought on to the pitch during a match in exchange for an existing player. Substitutions are generally made to replace a player who has become tired or injured, or who is performing poorly, or for tactical reasons. A player who has been substituted during a match takes no further part in the game, in games played under the standard International Football Association Board Laws of the Game.