Ultra-high-energy cosmic rays (UHECR) are the most energetic particles ever observed, having energies extending beyond 10^{20} eV. What astrophysical sources are responsible for their immense acceleration remains unknown despite decades of research. In this talk, I will investigate weather low-luminosity gamma-ray bursts (llGRBs), short-lived cosmic explosions currently seen as one of the most promising acceleration candidates, can be the main source of UHECR. Our study focuses on the radiation from the less energetic electrons, which are inevitably accelerated in the same region. This radiation can be characterized and compared to observations of llGRBs. We find that the radiation from these electrons would be much too luminous, showing that llGRBs would have to be orders of magnitude brighter if they hosted significant UHECR acceleration. This result challenges llGRBs as accelerators of UHECR.