A patent has been granted to Apple for an "electronic device having display with curved edges." The patent was filed in January 2016 and features a number of images that could easily be described as potential smartwatch displays. Producing a circular smartwatch would be something of a design departure for the Cupertino-based company.
https://www.notebookcheck.net/Apple-may-be-working-on-a-circular-shaped-smartwatch.302962.0.html