Let's think about what could be the potential problems if we include an indefinite progress indicator of the action button.
- Can symbolize the state of the action button is changing
Since the loading state comes soon after tapping the button and tied with it, the user may think the state of the action button is changing and would expect a different state for the button after loading disappears.
- Expecting, users would tap on the button more than once to stop ongoing activity
Since the loading state appears once user hits the button, the user may interact with the button again to stop the ongoing activity.
A disable state of a button might help ~ but won't recommend since it's your CTA and the user would be wondering why you disabled the button as they interact.
I am assuming you are loading a page once the user clicks on CTA.
- More clearer visual cue would be the center/top of the page.
Or you can show the loading stage through lazy loading feature.
If current page stays intact, till new page loads
The material design usually shows an indefinite progress state below the navigation. The design presented here has a constraint here because of the position of the fab button.
If you are thinking to keep it along with the navbar itself, the extreme bottom is the place to consider. Reminder ~ Visual cue should be strong
- Whatever you do, the next action must have some headers. You can explore that area as well.
A screenshot of few screens would have been helpful to decide on where to place.