Inclusion Criteria:  Documented COVID-19 pneumonia: defined as upper respiratory tract specimen (nasopharyngeal swab (NPS) or viral throat swab) positive for COVID-19 and/or imaging at computed tomography scan suggestive of COVID-19 pneumonia. Confirmed coronavirus (SARS-CoV-2) (positive real-time reverse transcription polymerase chain reaction test (RT-PCR) for SARS-CoV-2 within 72 hours) enrolled ≤ 48 hours of need for supplemental oxygen. Currently hospitalized requiring supplemental oxygen. Have severe COVID-19 according to the World Health Organization (WHO) Interim Guidance with confirmation by real-time RT-PCR assay. The enrollment criteria with one of the following: respiratory distress, respiratory rate (RR) ≥30 beats/min; oxygen saturation level less than 93% in resting state; or partial pressure of oxygen (PaO2)/oxygen concentration (FiO2) ≤ 300 mmHg. Willing and able to participate in all required evaluations and procedures.  Exclusion Criteria:  In the opinion of at least two investigators, unlikely to survive for >48 hours from screening. Severe chronic respiratory disease (e.g. Chronic obstructive pulmonary disease or other) requiring supplemental oxygen and/or having required mechanical ventilation pre-COVID-19 infection. Concurrent enrollment in a COVID related interventional drug trial. Use of remdesivir, steroids, and convalescent plasma are permitted along with other standard of care therapies for COVID.37 Currently on invasive mechanical ventilation. Hypotension defined as systolic blood pressure < 90 mmHg on two sequential readings at least 4 hours apart. Total Bilirubin ≤ 3 x upper limit of normal (ULN), Creatinine Clearance ≥ 30 mL/min/1.73m2. Pregnant or breastfeeding. Known diagnosis of an acute thrombosis on admission. Concurrent dual antithrombotic therapy (aspirin or P2Y12 inhibitor plus anticoagulation to treat deep venous thrombosis or pulmonary embolism (single antiplatelet or anticoagulant agent at prophylactic dose is permitted). Concomitant use of thrombolytic therapy. Concomitant therapeutic systemic anticoagulant therapy (e.g. heparin, warfarin, direct thrombin inhibitors and direct factor Xa inhibitors). As per NIH Guidelines: Hospitalized adults with COVID-19 should receive Venous thromboembolism (VTE) prophylaxis per the standard of care for other hospitalized adults (AIII). Anticoagulant or antiplatelet therapy should not be used to prevent arterial thrombosis outside of the usual standard of care for patients without COVID-19 (AIII); https://www.covid19treatmentguidelines.nih.gov/therapeutic-management/ History of recent major bleeding, defined in accordance with the criteria of the International Society on Thrombosis and Hemostasis (ISTH). History of bleeding disorder thought to impose excessive bleeding risk as per investigator discretion Hemodynamic instability, defined as inability to maintain mean arterial pressure. Hypersensitivity to the active substance or to any of the excipients of uproleselan. Any physical examination findings and/or history of any illness that, in the opinion of the investigator, might confound the results of the study or pose an additional risk to the patient by their participation in the study