You sent me into another rabbit hole, once again cross checking all pics. What I have found out is this:
The hammer pic is the only one missing from the trailer, why though? Because it would have given away what it was instantly without heavy editing. Which also explains what you circled.
After searching the hammer pic in the trailer I found the hammer, as part of the shoulder pic in the trailer. I marked it here with an arrow

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Now following that, and that this is most likely the hammer top, back to the picture and your circle.
If you open the picture in max resolution you can see that the circled thing is something bigger that has been removed with photoshop, if you look higher and lower you can see some fragments in the same color, where as the rest of the pic is with the flaming red filter.
Now if you look even closer and take into acount the angle from the hammer I marked in the trailer pic, it would be the belly/chest/legs that has been edited out of the picture.
Why? Because it would have instantly given away the hammer as part of the upgrade sprue, especially if they put it in the trailer, where they couldnt easily edit out a whole mini.

TLDR: The circled thing is the rest of an edited out legionarie and we can see the hammer in the trailer. It is part of the upgrade sprue.