Biddle, who turned 19 last week, has signed a two-year contract and will become Sydney FC's third Under-20 player for the Hyundai A-League 2007/08 season.

The club's other youngsters are defender Nikolas Tsattalios and striker Ben Vidaic.

"I'm very excited to be joining Sydney FC," said the young winger. "I'm just at the start of my footballing career and relishing the challenges that lie ahead."

Sydney FC coach Branko Culina is confident that Biddle, who will play his last game for Blacktown City Demons against Bankstown City at Penrith's CUA Stadium, will push for a place in the starting side.

"Adam is an exciting young player with tremendous potential," said Culina. "I'm sure he'll be knocking on the door for a spot in the team this season."