The Swiss Light Source (SLS) storage ring has been rebuilt as SLS 2.0, providing an electron beam with significantly reduced horizontal emittance. This upgrade enables an X-ray beam with brightness increased by nearly two orders of magnitude and extends the accessible photon energy range by approximately 50%. Precise characterization of the electron source is crucial for optimizing and fully exploiting the performance of new fourth-generation light sources. However, conventional methods for determining the electron beam source size, such as pinhole-based imaging, lack the resolution needed to characterize sub-10 µm beam sizes, thus motivating the development of advanced diagnostic approaches. Here, we employ a Fresnel zone plate (FZP) based system to measure the electron source size at the SLS 2.0 storage ring. We demonstrate the measurement of sub-10 µm electron beam sizes and discuss challenges and potential future improvements of the proposed monitor.