Bilbao will not be able to keep Williams for a long time and is facing with pressure from big clubs this summer. If they won't lose Williams this summer, they will lose him in future like next one, two or three seasons. Because Bilbao is a small club and in modern football, most of players are not loyal with a single club. They will move to bigger clubs to have better income from salary, shirt sales, advertisement rights and have better opportunities to win trophies.
Bilbao is definitely a small club and they sign players who don't play in big clubs in Europe but who start playing football at an early stage. Nico Williams has performed well in the Euro tournament and his age is so young that the big clubs in Europe are now eager to sign him.
Now that there is a good demand for this player in the market, even if he does not want to leave the club, this player should go to a big club in Europe. However, whichever club he decides to go to, he must make a thoughtful decision because if the club signs him now, he will be signing a long-term plan agreement, so he will not have much of a chance to leave the club until the end of the stipulated period. There are clubs who deal with young players and who have developed young players to a good stage in their careers, so Nico Williams should be interested in signing a contract with them.