Olympique de Marseille have moved to reinforce their defence by signing Spanish Under-21 right-back César Azpilicueta from CA Osasuna for a fee that could rise to €9.5m.

The French champions agreed a four-year deal with the 20-year-old, who said: "I'm very happy to be here. OM are a big side. I think I can achieve great things here. At Osasuna I had team-mates [Ludovic Delporte and Jaroslav Plašil] who knew Ligue 1 and told me good things about it."

Born in Pamplona, Azpilicueta rose through the Osasuna ranks before establishing a first-team place, going on to make 99 Liga appearances over three seasons. A winner at 2007 UEFA European Under-19 Championship with Spain he becomes the first signing of the summer for Marseille, who start the UEFA Champions League in the group stage.