The retailer, whose sentimental Christmas ads by Adam & Eve/DDB have become an anticipated annual event in popular culture, is believed to be behind the video.
The clip was published today by a Twitter account called @UndertheBed2017 which tweeted the video at 8.05am.
Last month John Lewis did not comment on speculation that this year's Christmas ad would feature a "big, cuddly monster".
The ad, which is due for release in the coming days, has been directed by Oscar-winning director Michel Gondry, Campaign revealed last month.
A John Lewis spokeswoman declined to comment on this story.