Snyder posted a black-and-white photo of Leto in character, his face blurred as the camera focuses on the joker playing card he holds in the foreground.
Addressing Leto and Suicide Squad director David Ayer, Snyder wrote: "Amazing character you created. Honored to have our worlds collide."
With most of Leto's body out of focus, it's hard to see exactly what we can expect this March - but even with the minimal detail we have, some fans reckon he reminds them of someone.
One tweeted: "Is it just me or this interpretation of Leto Joker looks a lot like Joaquin Phoenix's Joker?"
Someone else wrote: "Have they just dressed Jared Leto as Joaquin Phoenix and hoped nobody will notice?"
Another said they 'thought it was Phoenix' when scrolling through Twitter, while a fourth said: "His silhouette looks so much like Joaquin Phoenix's joker here."
Someone else added: "Who's the guy in the back meant to be? Because it ain't Jared Leto's Joker. It more looks like Joaquin Phoenix's Joker."
The 240-minute Zack Snyder's Justice League is an extended cut of the 2017 film, which suffered a difficult production after Snyder stepped down from the project following the death of his daughter, with Joss Whedon taking over in his place.
After a box-office disappointment and average reviews, fans petitioned for an alternate cut more faithful to Snyder's original vision - which Warner Bros decided to go for.
In May 2020, Snyder announced a new cut of the film would be released as Zack Snyder's Justice League.
Last month, it was confirmed the film would hit streaming service HBO Max in the US this March, with plans for the UK release yet to be announced.
A press release from Wonderland Restaurants, promoting its new Wonderland at Home launch, said: "Zack Snyder's Justice League will premiere on the 18th March and will drop on HBO Max in the US with UK release plans to follow."
The Wonderland at Home campaign marks a partnership between restaurant chain Wonderland Restaurants and Warner Bros, and is billed as 'a premium immersive boxed dining experience featuring some of the world's most iconic brands from film and television delivered to your door in 2021'.
Zack Snyder's Justice League is due to be released on HBO Max in the US on 18 March.Featured Image Credit: Warner Bros/HBO Max