When Leijer was 15 years old his family moved south to Jan Juc on Victoria's surf coast and attended Belmont High School where he joined Geelong SC and represented the U-15's Victorian Country team.

While still training at the VIS, Leijer and his future teammate Kristian Sarkies were selected to trial with Premier League Everton Football Club for three weeks.

His former VIS coach Ernie Merrick, who had taken the reins at Melbourne Victory, stated; "Adrian is a reliable and uncompromising defender with a football maturity beyond his years.

[1] Leijer consistently played for the Fulham reserve team throughout the 2007–2008 season and was also included in the squads to face both Liverpool and Reading, but stayed on the bench both times.

Whilst tipped by Fulham reserve coach Billy McKinlay to make a greater impact in the first team that season, Adrian missed most of the club's pre-season due to the Olympic tournament and only made the bench once, in a League Cup defeat to Burnley.

[4] After a promising start, slotting straight back in to the side hours after landing,[5] former captain Kevin Muscat commented on his potential to be a key figure in the club.

[12] During the 2019 mid season transfer window Adrian signed with National Premier Leagues Victoria side Dandenong City SC[13] and made his first appearance at the round 14 clash against Avondale FC.

Adrian Leijer's first taste of the senior international scene was when he was selected by Guus Hiddink to train with the Socceroos before the 2006 FIFA World Cup in Germany.