Dr Tim Parke, an emergency physician, warned that "all sorts of bad stuff starts to happen" when A&E units became overcrowded, and called on other hospital wards to be better prepared to accommodate an overspill of patients.
It comes after figures published earlier this week revealed winter deaths in Scotland rose to the highest level for four years between December 2012 and March 2013.
Dr Parke, an outspoken doctor who returned to NHS Greater Glasgow and Clyde earlier this year after working as the clinical director of the adult emergency department at Auckland City Hospital in New Zealand, said hospital bed shortages left A&E staff unable to cope.
Writing in his personal blog, he said: "Overcrowding is the single biggest threat facing emergency departments this winter. Once our departments get overcrowded, all sorts of bad stuff starts to happen.
"Most bad shifts in the emergency department, like a major accident producing a heavy multiple trauma load, or staff sickness causing crucial roster gaps, are surmountable, mostly, with hard work, multi-tasking, leadership, experience and team work.
"However, start a shift with patients on trolleys and no prospect of in-patient beds and it will be a shift of frustration, impotence, poor care and staff burn-out."
The Herald's NHS: Time for Action campaign has been highlighting the impact of bed and staff cuts on patient care.
Dr Parke, who is based at the Southern General hospital in Glasgow but stressed that he speaking in a personal capacity, added that overcrowding meant "treatments get missed or delayed" and "errors happen with mixed-up blood samples and wrong medication".
He urged other departments to share the load, as happens in other parts of the world.
He said: "Ward staff and specialists don't care too much about emergency department overcrowding as it doesn't really affect them. The solution may lie in reversing that through overcapacity protocols. Using these, when the emergency department becomes dangerously overcrowded, the wards share the risk and the pain by also taking patients in their corridors." Margaret Watt, chair of the Scotland Patients Association (SPA), said contingency plans should be in place to prepare departments for a worst-case scenario.
She said: "They should have been putting contingency plans in place months ago to cope with outbreaks of flu, gastroenteritis and so on. They should be looking at the amount of cases they had last year and adding on 5% as a worst-case scenario, then make sure there are sufficient resources in place to cope.
"We know these things happen and we should prepare for the worst. A&E shouldn't be overworked at that time of year, or any time."
Ms Watt added that the SPA had already seen the impact of overcrowding. She said: "Last month we had a woman who went to A&E with internal bleeding. They said she was fine and sent her home. She went back a second time but they sent her home again and when her husband asked why, they said they had 'no beds'. The third time she went in, she didn't come back out again.
"This shouldn't happen. If someone's coming back a second time their name should come up with a red line under it."
A spokeswoman for the Scottish Government said it had already launched a £50 million drive to improve emergency care across Scotland, including the roll-out of electronic whiteboards that allowed clinicians to track patients digitally through the entire hospital system.
She said: "We have already released £1.8 million of this funding to support the recruitment of 18 new A&E consultants, and a further £7 million has been released to boards to support additional beds, new clinical staff and innovative new approaches."