Leckie is ready for his first involvement at this year's tournament after his recovery from a hamstring problem that ruled him out of all three of Australia's Group B matches.
Arnold's side finished second in the group after defeat to Jordan preceded victories over Palestine and Syria, and Leckie is joined in the squad for the clash with Uzbekistan by fit-again defender Josh Risdon and by Trent Sainsbury, who was suspended for the Socceroos' final group game.
Arnold paid tribute to the Australia medical team for ensuring Leckie's availability, and said his side are ready to follow up their dramatic 3-2 win over Syria with another victory.
"The wonderful thing is Mathew Leckie is back and he will be on the bench," Arnold said. "It's like signing a new player halfway through a tournament. We planned when he got injured at Hertha Berlin that we needed to look at how the injury would come along.
"We were patient with that and our medical staff have done a great job getting him ready. And that, with his positive attitude and how he is in camp and in around the boys, has given the boys a lift already.
"Josh Risdon is back again, so he will be back, and Trent Sainsbury is back from suspension. Andrew Nabbout is the only one out at this stage so we're getting stronger and stronger as the tournament goes.
"We're into the last 16, so it's a step up in the competition and a step up in the tournament and I expect our team to step up another level as well.
"But we've analysed them and we expect to expose their weaknesses. They've had a three-day turnaround and we've had five so we're mentally fresh and feel great and are ready to go for this game."
Uzbekistan made sure of its progress to the knockout stages with victories over Oman and Turkmenistan in their first two Group F matches, before taking the lead against Japan only to lose 2-1.
Coach Hector Cuper promised some changes to his team but said there would be no diversion from the approach that has taken them beyond the group stage for the fifth consecutive tournament.
"We know the importance of tomorrow's game," said the former Valencia and Inter manager. "It's the knockout stage, so we have no room to make errors. We will come to the pitch to win, but at the same time we realise Australia are a tough rival and one of the best teams in Asia.
"During the last three days we have tried to improve on all of our mistakes and we have tried to analyse the Australia side. Based on their advantages, we will make some changes but it doesn't mean we're going to change the system or style of our game.
"We will come to the pitch and the players will do their best to get the necessary result."