The New Zealand club are in Perth preparing for the round 5 clash at nib Stadium but Herbert says there are no certainties for the starting line-up after his side lost 1-0 to Brisbane Roar last week.
The arrival of Nick Ward from Melbourne Victory had also posed some problems for Herbert.
"No, we haven't decided yet (on the team)," Herbert said. "We're going to wait till Saturday. It'll be a tough call come the weekend. With Nicky coming in we have to decide whether we'll bring him straight into the starting XI and we're still contemplating that. We have to get him accustomed to what we're about and how we want to play, but he's an intelligent guy with a good background in football and he'll slot in pretty quickly.
"There are a few (selection) headaches to go through over the next couple of days."
Herbert admitted that the league leading Glory will be a very hard team to beat but insists his Phoenix are ready for the challenge.
"They're a good strong side that probably got out of jail a wee bit (against Melbourne Heart) with a late penalty, and we all know about the repercussions of that with Michael Baird being suspended for two matches," he added.
"They're still getting the points. (Coach) Dave Mitchell has always got a good side and they'll be hard to beat. But we'll be ready for them."