Born in Hanover, West Germany, Vasilj started his professional career at Croatian club Hrvatski Dragovoljac in the 1995–96 season.

Prior to the World Cup, he made his international debut by appearing as a substitute goalkeeper in the second half of Croatia's friendly match against Slovakia played on 29 May 1998 in Pula.

He left Hrvatski Dragovoljac for Dinamo Zagreb in the summer of 1998, but was merely the club's third-choice goalkeeper and managed to make only two domestic league appearances in the following two seasons.

He subsequently did not win any international caps,[2] but was called up to be the Croatia national team's third-choice goalkeeper at the Euro 2004 finals in Portugal after the team's first-choice goalkeeper Stipe Pletikosa was forced to withdraw from the tournament due to an injury.

He left Dinamo in the summer of 2005 and joined Turkish club Konyaspor, where he spent the first part of the 2005–06 season as the second-choice goalkeeper, making only two appearances in the Süper Lig, and he subsequently went on to leave Konyaspor for NK Široki Brijeg from Bosnia and Herzegovina at the beginning of 2006, signing an 18-month contract until June 2007.