We investigated the relationship between cognitive functioning, work performance, and sleep in non-clinical burnout. In a working population, an online survey was conducted with additional online neuropsychological tests of varying complexity, measuring attention and different components of working memory, of which the coordinating subcomponent the ‘Central Executive’ is thought to be the most vulnerable to stress. Results indicate that non-clinical burnout is associated with more-though not severe-sleep problems, more depressive complaints, impaired work performance, and with both subjective and objective cognitive impairments. Compared with healthy respondents (N = 107), people with non-clinical burnout (N = 17) had a significantly poorer performance on the tests of the visuospatial sketchpad and the Central Executive of the working memory. Our study also indicates that more complex tests may be more sensitive in detecting cognitive dysfunction in non-clinical burnout. Furthermore, a relationship was found between dual-task performance and work performance. Regarding to sleep quality, in our sample of people with non-clinical burnout, there were no severe sleep problems. In the entire sample, however, insomnia was significantly related to subjective, but not objective, cognitive functioning, and also not to work performance.