According to leaks, the game is set during the Victorian era with players getting to travel on stagecoaches from the time.
An insider told gaming website Kotaku that the game will be out next year on PS4, Xbox One and PC.
The game's developer Ubisoft said: "It is always unfortunate when internal assets, not intended for public consumption, are leaked."
It's not been a good month for the video game developer.
Ubisoft has apologised after the latest Assassin's Creed was plagued with bugs and unexpected technical issues.
The French firm said it was providing the upcoming Dead Kings expansion pack for free to fix problems on Assassin's Creed Unity.
The leak shows a video with an assassin climbing up a tower and looking out over what looks like Victorian London.
It then shows some of the game's side activities; gambling in a pub and street-racing with carriages.
It seems the game's task is to kill a man named Roderick Bulmer, who has been trafficking young children for the assassins' ancestral enemies.
Ubisoft told PC Gamer: "While we certainly welcome anticipation for all of our upcoming titles, we're disappointed for our fans, and our development team, that this conceptual asset is now public.
"The team in our Quebec studio has been hard at work on the particular game in question for the past few years, and we're excited to officially unveil what the studio has been working on at a later date.
"In the meantime, our number one priority is enhancing the experience of Assassin's Creed Unity for players."
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Next year's Assassin's Creed will be set in London.