Chelsea have agreed a fee with Spanish club Valencia to sign Juan Mata for a reported £23.5m.
On Monday, the 23-year-old winger announced on Twitter that he was on his way to Stamford Bridge for a medical.
Mata tweeted: "Travel to London for medical examination, and come back to Valencia to say goodbye to everybody as you deserve... thanks so much."
The Stamford Bridge club said the deal was subject to Mata agreeing personal terms and passing a medical.
"An agreement has been reached with Valencia for the transfer of midfielder Juan Manuel Mata," said a statement on the Chelsea website.
Valencia had confirmed the deal themselves on Sunday.
No fee has been officially disclosed but reports in Spain suggest the Blues are paying £23.5m.
After Chelsea's 2-1 win over West Brom, boss Andre Villas-Boas said: "He can add to any squad in the world."
Mata has been at Valencia since 2007 and as captain helped Spain win the Under-21 European Championship in the summer. He was also part of Spain's 2010 World Cup winning squad.
Villas-Boas has previously spoken of the need to recruit more midfielders and the club have also made bids for Tottenham's Luka Modric.
On Saturday after Chelsea's 2-1 win against West Brom Villa-Boas was questioned about Mata.
He refused to be drawn on whether any deal was close, but he said: "He's a good player, a very good player.
"He's not our player but he's an interesting player.
"His curriculum speaks for itself. He's a player who scores and assists and he can add to any squad in the world."
Mata joined Valencia from Real Madrid's youth team. Last season, the 23-year-old midfielder, who is 5ft 7in tall, scored eight goals to help Valencia to a third-place finish in the Primera Liga.
He was also part of Spain's 2010 World Cup-winning squad and captain of the under-21 team that won the European Championship this year.
If Mata leaves, Valencia will have sold all four of their World Cup winners, with Mata following David Villa (Barcelona), David Silva (Manchester City) and Raul Albiol (Real Madrid) out of the club.