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.
How can Chelsea keep spending?
The 22-year-old's arrival takes Chelsea's January spending to £288m, according to transfer website Transfermarkt.
That follows an outlay of £292m in the summer - a record for a British club in the summer window - taking their total spend under new American owner Todd Boehly to £580m.
It is the joint-sixth most expensive signing 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.
Chelsea have signed Noni Madueke, Mykhailo Mudryk, David Datro Fofana, Andrey Santos, Benoit Badiashile and Malo Gusto on permanent deals in January.
They have also brought in Joao Felix on loan from Atletico Madrid.
The Blues are 10th in the Premier League, 10 points adrift of the competition's Champions League places after 20 matches.
The club was bought for £4.25bn by a consortium led by American investor Boehly last May, after previous owner Roman Abramovich was sanctioned over his links to Russian president Vladimir Putin.
BDST: 1307 HRS, FEB 1, 2023