Del Piero was unable to return after half-time in Sunday's 2-1 win over Melbourne Heart due to lower back tightness.

It was the third time the 39-year-old has failed to complete a match through injury this season, while he has also missed two full games.

Emerton made his return from several weeks on the sideline with a leg injury against the Heart off the bench but will not back up against the Phoenix.

"It looks as though Alessandro and Brett will miss this one," coach Frank Farina said on Friday.

"It's nothing bad or long term but with the travel and particularly with (a game against) Brisbane four days later it's probably not worth the risk."

The third-placed Sky Blues head across the Tasman as favourites to claim their seventh victory of the season against the winless Phoenix who are languishing in ninth spot.

But Farina says there is no room for complacency against Ernie Merrick's men.

"Without doubt, it's a banana skin, dangerous game, whatever you want to call it," he said.

"It's a difficult one and they're playing quite well.

"They were dead unlucky last night (in their 1-0 loss) against Central Coast and they haven't won a game, so we're going to have to be at our best if we're going to get something over there."

Defender Sebastian Ryall, who will play is 100th senior game for Sydney FC against the Phoenix, echoed Farina's sentiments.

"I think they've been a bit unlucky, they played last night and they had some really good chances, they missed a penalty," Ryall said.

"They're a good side, I think we were actually quite lucky to get a result last time against them at home, so we're not expecting an easy match.

"They're going to be really fighting for their lives to get the win."

Ryall is the sixth Sky Blues player to reach 100 games for the club, consisting of 96 A-League appearances and three Asian Champions League fixtures.

He joins Terry McFlynn (190 games), Clint Bolton (125), Steve Corica (123), Alex Brosque (110) and Iain Fyfe (104) in the 100-games club for Sydney FC.

"I'm a Sydney boy so to make 100 games for this club, I'm proud about that," Ryall said.

"As a supporter of the club from day one and watching Dwight Yorke in the crowd, and now to play for them is quite special."