Sydney FC has been struck by injury again with talented midfielder Terry Antonis sidelined for the next month with a knee injury.

The 17-year-old sustained the injury during last Friday night's National Youth League match against Adelaide United at Hindmarsh Stadium with scans confirming damage to the cartilage in his right knee.

Antonis will rest before beginning a rehabilitation program.

"It is disappointing for me because I love playing. I have learnt a lot this season and I guess this is another part of football. I will be patient and do what the staff say and work back into it," Antonis said.

"We have some big games coming up which we need to win to make the top six so it will be weird having to watch but I know the boys can do it.

"The month will feel like a lot more but like I said, I must be patient."