The Heart are enjoying a resurgence in form with 10 points from a possible 12 to roar back into contention for the finals.
And they can move closer to the top six with a victory over the sixth-placed Wellington Phoenix on Sunday.
But they will have to achieve the result without Kewell, who will also miss next weekend's match against Brisbane Roar due to the injury he suffered in the second half of last week's win over Perth Glory.
"There's going to be a change with Harry, Harry's not going to be available, so we'll have someone else playing up front," Heart coach John van 't Schip said.
"Harry has a problem with his foot. Hopefully he's going to be back in 10 days, let's just say, so I don't think Brisbane is going to be on the program for now. Hopefully he can recover quickly from that and we'll keep him working hard in conditioning, doing the things he can do.
"It's a problem that has to rest. It's something that can't be forced in getting him on to the pitch, he needs a period of rest and he can kick off again from there."
Super-sub David Williams could be the man to replace Kewell up front after he scored the winner against the Glory last week.
One man who will definitely return to the side is marquee midfielder Orlando Engelaar after the 35-year-old missed the trip to Perth due to suspension.
"There are a few possibilities we can do," he said.
"We don't want to change that much in terms of positions but if players are not available then of course we will.
"Looking at the squad we've seen players come in do exceptionally well. Benny Garuccio has come in and done well, David (Williams) has done well, Nicky Kalmar also.
"That's all very positive in that if we have to replace a player or if a player is not in form then we have players who can step in and give the team a good help."
