Enzo Jeremías Fernández (born 17 January 2001) 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.

Born in San Martín, Buenos Aires, to Raúl and Marta; Fernández has four brothers, Seba, Rodri, Maxi and Gonza. He was introduced to football at a young age, playing for a local side called Club La Recova, before joining River Plate. It is unclear exactly when Fernández joined River Plate; in November 2019, in an interview for the River Plate website, he claimed to have joined the academy in 2005, in September 2020, Argentine newspaper Clarín reported that he joined River in 2006, while in February 2023, he claimed he was six when he joined in an interview for the Chelsea website, which would have most likely been in 2007.

He progressed through the youth ranks, and was promoted into the club's first-team by manager Marcelo Gallardo on 27 January 2019, in a 3–1 home loss to Patronato in the Primera División, despite remaining on the bench. He made his first-team debut on 4 March 2020, replacing Santiago Sosa in the 75th minute of a 3–0 loss to LDU Quito in the Copa Libertadores. In the weeks prior, he scored once, in the 6–1 thrashing of Libertad, in four games at the 2020 U-20 Copa Libertadores in Paraguay.

Despite being sporadically used Fernández's manager advised him to leave the club on loan, in order to continue his development. In August, Fernández was loaned to fellow top-flight club Defensa y Justicia. He made his debut for the Halcón on 18 September by manager Hernán Crespo in a 3–0 win over Delfín in the Copa Libertadores. Despite initially not being a starter, his performances impressed his manager and eventually he earned a place in the team, helping the club win the 2020 Copa Sudamericana, starting in the 3–0 win over fellow Argentinian side Lanús in the final, winning his first career title.

After impressing on loan, Fernández returned to River Plate, during the season at the request of manager Marcelo Gallardo, making his return on 15 July 2021, in the first leg of Copa Libertadores round-of-16, featuring in the 1–1 home draw to fellow Argentinian side Argentinos Juniors. He immediately became a starter and on 14 August, he scored his first goal for the club and provided an assist in a 2–0 win over Vélez Sarsfield in the Primera División. On 20 December, he agreed to a contract extension to 2025. Following a promising start in the 2022 season, which he scored eight goals and provided six assists in 19 games, Fernández was named the best active footballer in Argentina, being subsequently scouted by a number of established European teams.

On 23 June 2022, River Plate reached an agreement with Primeira Liga team Benfica for the transfer of Fernández for a €10 million fee for 75% of his economic rights plus €8 million in add-ons, but with the player remaining at River Plate until the end of the club's Copa Libertadores campaign. Following River Plate's round of 16 exit from the Copa Libertadores, on 14 July, Benfica confirmed the deal, giving Fernández the number 13 shirt, previously worn by club legend Eusébio.