#1 Diego Costa
Widely feared for his vicious nature, Diego Costa spent the 2007-08 season on loan at Celta de Vigo partly under the tutelage of former Ballon d'Or winner Hristo Stoichkov, who underwent a short disappointing stint as manager.
In fact, all three forwards present in Spain's 2018 World Cup squad - Costa, Rodrigo and Aspas - were at Celta in 2007-08. The reason he was sent out on loan was because Atlético Madrid had no space for another striker with Diego Forlán, Sergio Agüero, José Antonio Reyes, Luis García and Simão Sabros all on their books in 2007.
During his time at Celta, the Spanish international improved his style of play, netting six goals in a total of 30 appearances. In spite of his contribution, Costa's aggressive manner earned him a reputation for being a disruptive influence.