"His support for the al-Qaeda organisation is what we intend to prove"
Air Force Colonel Morris Davis,
Discussions on a plea deal began in January but both sides have declined to reveal the terms of any proposals.
Hicks, 31, a former kangaroo skinner and a convert to Islam, has been accused of training at al-Qaeda camps in Afghanistan and briefly fighting alongside the Taliban following the attacks on the World Trade Centre on September 11, 2001.
He has been awaiting trial at the camp since January 2002 and is due to face a pre-trial arraignment hearing on a war-crime charge on Monday.
His lawyers say they expect him to plead innocent if he is required to enter a plea to the charge of providing material support for terrorism, allegations the US is keen to prove.
"His support for the al-Qaeda organisation is what we intend to prove," Air Force Colonel Morris Davis, the chief prosecutor for the tribunals, said.
If convicted, Hicks could be sentenced to life in prison but Davis said he plans to use the case of John Walker Lindh, the American-born Taliban soldier who was given a 20-year sentence, as a precedent.
Hicks has previously appeared before an earlier military tribunal system created by a presidential order, which the US Supreme Court later ruled unconstitutional.
Last year however the then Republican-controlled US Congress last year, then under a Republican majority, passed a law authorising a reconstituted tribunal regime with some adjustments but still operating outside of regular US courts or military courts-martial.
The commission law allows for hearsay, evidence obtained through "coercion" and bars detainees from appealing their detention in US courts.
Speaking to reporters at Guantanamo, McLeod said his client was showing signs of weariness after five years of living alone in a small cell.
He had sunken eyes and has grown his hair long to protect his eyes from the light inside his prison cell, he said.
"He's not going to be the same person I saw three years ago. We've got to brace ourselves for that bit"
David Hicks' father
"He recognises the process ... is one that's designed to achieve convictions," he added.
Hicks' father, Terry, who was scheduled to arrive in Cuba on Monday with his daughter, Stephanie, said he was apprehensive about the reunion after hearing about his son's mental health.
"He's not going to be the same person I saw three years ago. We've got to brace ourselves for that bit," he said.
US and Australian officials have said that Hicks could serve his sentence in Australia.
John Howard, Australia's prime minister, has pushed Washington to deal with Hicks' case more quickly.