Although many vaccines have been approved for COVID-19, the continuing high incidence motivates the importance of drug repositioning. Among COVID-19 multiple complications, severe pneumonia and thromboembolism-related death are the most aggressive. We aimed to monitor the mechanisms by which SARS-CoV-2 led to severe illness and death to explore targets for therapies. Our objective was achieved by determining the cut-off of the novel biomarker human platelet membrane glycoproteins IIb/IIIa (CD41/CD61) (GPIIb/IIIa) in microparticle free plasma separated from peripheral blood samples of COVID-19 patients and healthy subjects using the ELISA technique. In comparison with the control, we observed an elevated level of GPIIb/IIIa in COVID-19 patients, especially those with severe illness including severe pneumonia and pulmonary embolism. Our data indicate the relevance of determination of GPIIb/IIIa as a diagnostic and prognostic biomarker for haematological complications including platelet aggregation and pulmonary embolism in COVID-19 patients suffering from severe illness. We conclude that determination of GPIIb/IIIa level by an easy, reliable, and low-cost ELISA kit helps in early diagnosis of haematological complications in COVID-19 patients and may help in improving the clinical outcomes and treatment of COVID-19 patients. Adding GPIIb/IIIa inhibitors (synthetic or natural products) to the treatment protocol of COVID-19 patients may add benefit in improving the clinical outcomes of COVID-19 patients.