The 21-year-old was shooting a fight scene on location in Southend, Essex when a gust of wind threw him off balance and caused the accident, according to The Mirror.
It is thought that the man was standing in for actor Neil McDermott for scenes which see his character Ryan Malloy clash with evil pimp Rob Grayson after tracking him down in the seaside resort.
Discussing the accident, a source told the newspaper: "The two come to blows, but the scene went wrong and one of them fell off. I heard one of the paramedics say that he was moving, but it looked like a very serious incident."
The stuntman was reportedly taken to Queen's Hospital in Romford after the accident and was said to be in a critical condition last night.
An EastEnders spokesperson said: "We can confirm that a stuntman was injured. We all wish him a speedy recovery."
In the storyline, Ryan's half-sister Whitney Dean (Shona McGarty) was groomed by Rob earlier this year, leaving the barman furious when he later found out what had happened. Jody Latham has reprised his role as Rob to conclude the plot.
EastEnders legend June Brown has also been filming in Southend for scenes which see her character Dot Branning reunited with estranged sister Rose.
> Read our EastEnders spoilers and news