Darren, 47, was struggled to adapt to life after leaving the army and, as a result, was a regular at the top of Waverley Steps begging for change.
Mr Greenfield, known to friends and family as Dan, served with the Royal Tank Regiment in Bosnia during conflict in the 1990s, also spending time with the Royal Army Pay Corps and Adjutant General’s Corps.
He was rushed to hospital on December 17 last year after contracting an infection as a result of long-term health problems while sleeping rough on the street, but died later that day.
Now, the Ancre Somme Association Scotland, an organisation which offers education, remembrance and supports Armed Forces charities, has begun a campaign to raise £7,000 to give Darren the send-off he deserves.
Tommy Davidson, secretary of the association, said: “When we saw Darren’s story we were very passionate and knew we had to do something. Darren served in Bosnia and we feel we needed to do something to help.
“We have raised £330 so far but we are determined to raise the campaign’s profile and reach the target.
“We just want to do our best for Darren and his family. He deserves to be honoured and remembered for sacrificing his life for us all. Now it is our turn to give something back.”
Friends have left floral tributes at the entrance to the steps, describing Mr Greenfield as “good as gold”.
His sister, Aston Robertson, said the experience in the Balkans was his “downfall”, leaving the former private school pupil with post traumatic stress disorder (PTSD).
Mr Davidson added: “PTSD is very common in ex-servicemen. A lot of people do not realise what it is does to you mentally. Unless you’ve seen war or conflict, you won’t fully understand. Unfortunately Darren came back and didn’t manage to get his life back on track.
“I left the forces 20 years ago and I was left to my own devices to find a job and fit back into life back home.”
Speaking to BBC Scotland’s Stephen Jardine programme, Aston described Mr Greenfield as her “hero”, adding that he received no help after leaving the forces. She said: “I feel the damage was already done, if he had got help in the beginning it would have been a lot better.”
Mr Davidson has contacted the association’s ambassador, Alexander Stewart MSP, to ask parliament for cross-party support to improve the care and support given to veterans once they leave the forces.
He said: “We need to make sure the people who serve our country don’t end up on the streets. They should get the support they deserve when they return. Everyone needs to play a part in changing the way we treat former soldiers. It’s a disgrace that they’re not treated as heroes. They should not end up on the streets like Darren did.”
To donate to Darren’s funeral, go to http://bit.ly/2G4bX1Z