is an Argentine professional footballer who plays as a midfielder for Premier League club Chelsea and the Argentina national team. Primarily a central midfielder, he is also capable of playing as a defensive or attacking midfielder.

As an academy graduate of River Plate, Fernández made his first-team debut for the club in 2019, before spending two seasons on loan with Defensa y Justicia. There, he won the Copa Sudamericana and Recopa Sudamericana, and returned to River Plate in 2021. He joined Benfica in the summer of 2022. Having played only six months for them, he joined Chelsea in January 2023 for a British-record transfer fee worth €121 million (£106.8 million).

An Argentine international, Fernández previously represented his country at under-18 level before making his senior international debut. He represented Argentina at the 2022 FIFA World Cup, playing an important role in helping his country win their third title, while also winning the tournament's Young Player Award. He also won the 2024 Copa América.