Andy Hadlington saw the mysterious blob silently hovering around and filmed it from the window of his office.
The mysterious grey object glided around the residential area of Knowle, Bristol, at 5.30pm on Sunday without making a sound.
UFO experts have been trying to verify the sighting and are hoping to speak to more witnesses and views of the eerie episode.
Computer game writer Andy, 36, said: "It was the freakiest thing I have ever seen in my life. I was sitting in my office and saw it out of the corner of my eye.
"We're not far from the airport so I thought it could even have been a low-flying plane, so I was quite alarmed.
"It was quite exciting - it sort of hovered past the houses. There was no sound. I ran downstairs and out of the garden to see where it went but I couldn't see anything.
"My fiancée was out at the time but I'm sure other people must have seen it. It was so clear."
Denis Plunkett, of the British Flying Saucer Bureau, based in Winterbourne, near Bristol, was unable to comment on the video but said there were ways to verify its authenticity.
Mr Plunkett, 78, said: "There are ways to sort out good from bad. Firstly they are silent, there will be no noise.
"They can also become invisible. They can go in and out of MoD radar. They can change speed, direction and height in seconds.
"The best thing is if there are multiple witnesses to the sighting. If more people saw this I'd be very interested."
NOTE: I really don't know what to say about this video though the source seems credible. I'll withhold any judgement until the investigation concludes, though I'm leaning towards CGI at this time. Stay tuned...Lon