Coronavirus 2 is responsible for Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2), and the main sequela is persistent fatigue. Post-viral fatigue is common and affects patients with mild, asymptomatic coronavirus disease-2019 (COVID-19). However, the exact mechanisms involved in developing post-COVID-19 fatigue remain unclear. Furthermore, physical and cognitive impairments in these individuals have been widely described. Therefore, this review aims to summarize and propose tools from a multifaceted perspective to assess COVID-19 infection. Herein, we point out the instruments that can be used to assess fatigue in long-term COVID-19: fatigue in a subjective manner or fatigability in an objective manner. For physical and mental fatigue, structured questionnaires were used to assess perceived symptoms, and physical and cognitive performance assessment tests were used to measure fatigability using reduced performance. •Fatigue is the main sequela of long COVID-19 and needs follow-up.•There are physical and mental manifestations of fatigue in long COVID-19.•This review presents the most used instruments in assessing fatigue in long COVID-19.•Muscle strength, walking, and functional tests assess physical fatigue in long COVID-19.•Executive function psychological tests assess mental fatigue in long COVID-19.