Objective We aimed to assess the interplay between functional impairment and anxiety, depression, and problematic Internet use levels in front-line healthcare workers who work in inpatient clinics of coronavirus disease-2019 (COVID-19) during the COVID-19 pandemic. Methods Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), Internet Addiction Test (IAT), and Sheehan Disability Scale (SDS) were administered to assess the depression, anxiety, problematic Internet use, and functional impairment levels of the participants. Results Two hundred thirteen participants were enrolled in the present study. Medical doctors showed significantly higher scores of IAT than the nurses and other medical staff (Kruskal–Wallis=6.519, p=0.038). Levels of SDS total are significantly correlated with scores of IAT (r=0.257, p<0.001), BDI (r=0.383, p<0.001), and BAI (r=0.308, p<0.001). All subdomain scores of SDS (social, family, work) and total scores of SDS were significantly and positively correlated with BAI, BDI, and IAT scores (p<0.05). In the separation mediation analysis, problematic Internet use partially mediated the relationship between anxiety-depression and global functional impairment. Conclusion Health politicians should produce policies to develop strategies for coping with consequences of anxiety and depression in healthcare professionals during any health crisis. In addition, we should raise healthcare professionals’ awareness that problematic Internet use is not suitable for dealing with anxiety and depression and may even lead to increase of functional loss.