Mr Greste was freed from prison and deported on Sunday after 400 days behind bars. He is now in Cyprus, en route to Australia.
Mr Greste, Mohamed Fahmy and Baher Mohamed were arrested in 2013 on charges of spreading false news and aiding the Muslim Brotherhood.
Mr Fahmy and Mr Mohamed remain jailed.
In an interview with al-Jazeera, Mr Greste described his release as "a massive step forward" for the Egyptian authorities.
"I just hope that Egypt keeps going down that path with the others," the Australian journalist added.
Mr Fahmy, who holds dual Egyptian and Canadian citizenship, could be freed if he renounces his Egyptian nationality, presidential sources say.
Canadian Foreign Minister John Baird said on Monday that Mr Fahmy's release was "imminent", without elaborating.
But there are still concerns about Mr Mohamed, an Egyptian who holds no dual nationality.
Speaking on Monday, Mr Greste said he "wasn't expecting" his release on Sunday and had been released with what felt like "just a few minutes' notice".
He described a "real mix of emotions" after learning he would be freed, with both a "sense of relief and excitement but also real stress in having to say goodbye to my colleagues and friends - people who've really become family inside that prison".
"It was a very difficult moment walking out of that prison. Saying goodbye to those guys, not knowing how much longer they would have to put up with this."
He expressed concern for Mr Fahmy and Mr Mohamed, as well as other journalists convicted in absentia.
"If it's right for me to be free then it's right for all of them to be free," he said.
Mr Greste, Mr Fahmy and Mr Mohamed, journalists for al-Jazeera English, were arrested in 2013 after being accused of collaborating with the banned Muslim Brotherhood after the overthrow of former President Mohammed Morsi by the military.
All three denied the charges against them and said their trial was a sham.
In June last year, Mr Fahmy and Mr Greste were sentenced to seven years in prison and Mr Mohamed to 10. Their sentences sparked an international outcry.
The three men's convictions were overturned on 1 January but they remained in custody pending a retrial.
Several students have also been held in the same case. The students deny working for Al-Jazeera but it is thought that material filmed on their phones was used by the network.
In a separate case, Abdullah El-Shamy, a journalist for Al-Jazeera's Arabic channel, was arrested in August 2013 when police broke up a protest by supporters of Mr Morsi.
He was released on health grounds in June 2014 after a hunger strike of nearly five months.
According to campaign group Reporters Without Borders, there are currently 165 journalists imprisoned around the world, including 15 in Egypt.
Muted reaction in Egypt media
How journalists were jailed in Egypt
Who are the jailed journalists?

Irfan Rabbani will join the SNP opposition group on the council, which Labour controls with a majority of 15.
The 49-year-old said he would not be standing in the local elections in May although he would be campaigning for other SNP candidates.
Mr Rabbani has represented Glasgow's Pollokshields ward since 2007. He had been a Labour member for 20 years.
Al-Jazeera journalist Peter Greste says he is relieved to be free but feels "incredible angst" at leaving behind two of his colleagues in jail in Egypt.
[NEXT_CONCEPT]
A Labour councillor in Glasgow who had been de-selected by the party has defected to the SNP.