The emerging 19-year-old is set to miss the Reds' remaining minor round games with a knee injury and leaves a hole in the team's defence.

Former captain Michael Valkanis slotted into the line-up in the second half against the Jets but coach Aurelio Vidmar gave no guarantees the veteran would be promoted to the starting line-up for the catch-up contest.

"Got a couple of options. We could put Robbie Cornthwaite back there, we can leave Robbie in the middle and we've got Michael (Valkanis) or Angelo (Costanzo) who can go into the centre of defence," said Vidmar.

"We've got Alemao as well who can play as a right back."

While Mullen's knee will keep him out of action, Lucas Pantelis's knee, which he damaged about two months ago, isn't causing any problems for the vice-captain.

In his first game back from injury he scored the match-winner against the Jets last Friday.

Despite his sparkling return to the side, Vidmar has realistic expectations for Pantelis against the Roar.

"Generally from experiences, someone who has been out for a couple of months comes back and plays close to 90 minutes, the following game can be a bit of a low," he said.

"We just have to monitor him. He was great at training so he's pulled up without any soreness or without pain so that's a fantastic plus for us."

The other player who's grabbed the coach's attention is Paul Agostino. The marquee player is clocking up some solid minutes in the National Youth League team and says he's ready for a comeback.

Vidmar hasn't ruled out the 33-year-old getting a promotion soon.

"He's in the mix with everyone else in terms of who's going to play and who's going to be in squad," he said.

"The most encouraging thing for Ago at this point in time is that he's been able to play three games in the youth league and get some match fitness and he's injury free and that's a real bonus coming towards the end of the season.

"He certainly brings a presence to the team, there's no question about that, whether we decide to do that or not is another question."

The clash against Roar will be held in balmy conditions but Vidmar was optimistic the heat and the players' recent heavy workload wouldn't affect their performance.

"We gave them the weekend off so we actually worked them reasonably hard on top of that and we've had the games," he said.

"They came back yesterday and they didn't miss a beat. I was really happy with the way the training went.

"I think they've been feeling quite good. I don't think that's a problem. The main concern for us is that we get our game right because we are up against a quality opposition."