Benfica have agreed a deal to sign Darwin Nunez from Almeria for 25 million euros.
Talks between the two clubs lasted several weeks but a record-breaking transfer has now been finalised.
Nunez's move to Benfica is the biggest sale any club in the second division of Spanish football has ever made.
Jimmy Floyd Hasselbaink had held the previous record for the last 20 years, having joined Chelsea for 23 million euros from Atletico Madrid in 2000.
Nunez is also the most expensive sale in Almeria's history, beating Felipe Melo's eight million euro move to Fiorentina in 2009, and the most expensive transfer in Benfica's history, surpassing the 22 million euros spent to sign Raul Jimenez from Atletico Madrid.