Chelsea have agreed a British record 121m euro (£107m) deal for Benfica's Argentina midfielder Enzo Fernandez.
The deal eclipses the £100m Manchester City paid for Jack Grealish in 2021.
Benfica said in a statement it had "reached an agreement with Chelsea FC for the sale of all the rights of the player Enzo Fernandez".
Fernandez, who only joined Benfica for a reported £10m in August, was named young player of the tournament during Argentina's World Cup triumph in Qatar.
The 22-year-old's arrival takes Chelsea's January spending to £288m, according to transfer website Transfermarkt.
That follows an outlay of around £270m in the summer - a record for a British club in the summer window - taking their total spend under new American owner Todd Boehly to more than £550m on 17 new players.
The Fernandez signing is the joint-sixth most expensive of all-time, equalling the 120m euros Barcelona paid for France forward Antoine Griezmann in 2019.
Fernandez, signed by Benfica from Argentine side River Plate, has scored four goals in 29 appearances for the Primeira Liga side.
He scored once during the World Cup, netting Argentina's second goal in their 2-0 group-stage win over Mexico.