The World Game understands that the Sky Blues were alerted to a clause in Buhagiar's deal that gave the 20-year old an option to be released if the Mariners parted ways with their previous coach, Paul Okon.
Buhagiar, one of the Mariners' few shining lights in an awful season for the Gosford-based club, has made a major impression across the league with his pace and work rate.
He also has six caps for the Australian Under-23 team.
The news is a frustrating blow to new Mariners' coach Mike Mulvey, who has already set forth an agenda of re-connecting the club to the local community and promoting local talent.
Buhagiar was not only born in Gosford but supported the Mariners growing up, in addition to playing his youth football at Umina Eagles and attending the International Football School at Kariong.
It is understood Mulvey made two final pleas to keep Buhagiar but was informed that the forward had already made his mind up to leave before the coach's appointment was concluded.
The Mariners are already on the lookout for several new recruits, having shown no mercy to much of the under-performing squad from last season, announcing the release of Liam Rose, Storm Roux, Jacob Poscoliero, Josh Bingham, Blake Powell and Peter Skapetis, whilst not renewing Tom Glover's loan deal from Tottenham Hotspur.
Roux is expected to join Melbourne Victory in the coming weeks and Rose, a once highly-touted junior, is likely to attract interest from elsewhere.