Premier League - Valencia: Mata joining Chelsea
Mata is reported to have spoken with Chelsea manager Andre Villas-Boas on Friday and he is expected to join the Premier League club for a fee of 27 million euros (£23.5m)
The 23-year-old, who will likely be asked to play in one of the advanced wide positions in Chelsea's 4-3-3 formation, will now undergo a medical in London.
A statement on Valencia's official website read: "Valencia Football Club has reached an agreement in principle with Chelsea FC for the transfer of the player Juan Manuel Mata.
"The agreement is subject to the relevant medical tests."
Mata has been the subject of interest from both Arsenal and Tottenham this summer but he is now heading to Stamford Bridge as Chelsea's fourth signing of the window.
The midfielder will join compatriot Oriol Romeu and Belgian youngsters Romelu Lukaku and Thibaut Courtois in signing for the club if he completes his move to West London.
Mata was a product of the Real Madrid youth set-up but joined Valencia in 2007 in search of regular first-team football.
Over the past four seasons he has proven to be a real asset for Valencia and last season scored eight times and claimed 12 assists following the sales of David Villa to Barcelona and David Silva to Manchester City.
Mata was a member of the Spain squad that won the World Cup in 2010 and the European Under-21 Championships this summer.