Evening News sources said the man, named locally as Ronnie McGhie, was working the late shift on Saturday 5 October when the crush happened.
Sources say he is now in a coma in hospital after reportedly suffering significant injuries including broken ribs, a broken hib and a broken leg.
It is understood a major internal health and safety investigation is underway at Lothian before a full report is submitted to the Health and Safety Executive.
The accident, at around 8pm on Saturday, took place after Mr McGhie had been driving a bus due to be refuelled inside Lothian’s Annandale Street depot.
'He Panicked and Tried to push the bus'
Sources say the mechanic stopped the bus behind another bus before stepping out of the vehicle.
The bus then began to roll forward towards the other bus, with Mr McGhie jumping between the two in a desperate attempt to stop them colliding, resulting in the devastating crush.
One source, who wished to remain anonymous, said: “Ronnie jumped onto a bus and moved it forward but had to stop as there was a bus in front of him.
“He stopped and was ready to move when someone told him something. Ronnie could not hear what was said so he jumped off the bus not realising he forgot to put the brakes on.
“When off the bus he noticed the bus moving forward and he panicked and tried to push the bus at the front.
“Seconds it took and the bus pushed Ronnie into another bus and he was struggling for air with a 10 ton bus.”
A Lothian spokesman said: “We can confirm that a member of our team was involved in an incident within our Central garage on Saturday evening.
“Our thoughts are with our employee and his family at this difficult time.”
Police Scotland confirmed they attended the incident at around 8.10pm on Saturday.
The Scottish Ambulance Service have also been contacted for comment.