Sydney FC coach Graham Arnold believes defender Aaron Calver has a big future at the club after the Helensburgh teenager's appearance as a substitute in the Sky Blues' pre-season friendly against Wellington Phoenix on Friday night.

Calver replaced fellow Illawarra product Pedj Bojic in the second half of the 0-0 draw at WIN Stadium.

The 18-year-old has already made nine appearances for the club in the A-League and Arnold is adamant he will add to that tally this season.

Sydney FC begin their A-League campaign against Melbourne City at home on October 11.

"He had a couple of games for Sydney FC before I came here," the new coach said.

"He played against Canberra and was excellent. [Friday] was a step up in level and he handled that.

"This year is more about him getting stronger. He will get game time for sure in the first team at some stage.

"He is a guy who takes everything on board. He is open to learn and that is the most important thing.

"He is a good athlete and he has got good size and he is very good on the ball.

"So far I am very happy with him."

Calver joined another Illawarra junior in the back line as Matt Jurman put in a 90-minute shift at left-back.

Seventeen-year-old fullback Alex Gersbach was out injured for the pre-season clash, allowing Jurman to see some uncontested game time.

"Those two [Jurman and Gersbach] are fighting for that position at the moment but the beauty of having Matty Jurman is that he can play centre-back as well ... left and right," Arnold said.

"I am very happy with Matty Jurman. I think he is a very underrated player. He is a guy who has already won two championships but no-one reads about that, so he knows how to win things.

"You know he can handle the big stage."

Jurman, who has won titles with Sydney FC and Brisbane Roar, said he was happy to play anywhere in the back four.

His presence, alongside Bojic, Nikola Petkovic and Seb Ryall, saw the Sky Blues secure their third straight clean sheet against the Phoenix.

"It is always positive for us at the back to get a clean sheet. Arnie wants us to be hard to beat at the back first before we start scoring goals," Jurman said.

"Saying that, we have scored a lot of goals in pre-season so that has been positive as well.

"If we can keep a clean sheet it gives us a good opportunity to win the game."

The Sky Blues will continue their FFA Cup campaign on Tuesday night when they face Sydney United at Sydney United Sports Centre in a round of 16 clash.

"It is a big game for us. We want to win it. We have to be careful because Sydney United are a good team as well," Jurman said.

"It is going to be a big game so hopefully a lot of fans come out.

"I am sure all the boys are looking forward to it ... I can't wait to be honest."