The highly rated Croatian midfielder has been linked to Liverpool and Tottenham Hotspur previously.
The youngster is highly rated in Croatia and is the only teenager named in their squad for Euro 2016 this summer.
He was in impressive form last season, scoring five goals and bagging six assists, and that form has caught the eye of several European sides.
As far as they are concerned, the youngster could be tempted into the move as he knows that the Hammers are willing to give youngsters a chance in the first-team.
Slaven Bilic’s side are not only the only Premier League team keen on him though, with Liverpool and Tottenham Hotspur both having been credited with an interest.