Athletic Bilbao have agreed a contract extension with rising teenage star Iker Muniain.

The 16-year-old midfielder, who became the youngest scorer in Primera Division history when he netted Athletic's equaliser in the 2-2 draw with Real Valladolid earlier this season, will now be tied to the Basque giants until 30 June 30 2015.

The buy-out clause in the Spain under-17 international's contract is believed to be between €36 and 45million, depending on how well he does.