A study was conducted to characterise hemi-diaphragm elevation on interval chest x-ray (CXR) follow-up of patients following their COVID-19 pneumonia illness. A total of 467 patients with COVID-19 pneumonia were screened and 19 patients (4.1%) of these had an elevated hemi-diaphragm. The patients of interest were the 15 patients (3.2%) that had new elevation of the hemi-diaphragm noted on CXR. This abnormality persisted after an average follow-up of seven months from SARS-CoV-2 PCR detection. Patients reporting symptoms suggestive of diaphragmatic weakness underwent diaphragm ultrasound (12 patients), pulmonary function tests (10 patients), muscle function (six patients) and neurophysiology (five patients) to investigate phrenic nerve function. Ultrasound confirmed reduced/paradoxical diaphragmatic movements in eight patients, four of whom also had reduced thickening fraction. Neurophysiology peripheral limb studies on five patients did not support the differential diagnoses of critical illness neuropathy/myopathy. We propose that in selected patients, COVID-19 may cause phrenic nerve mononeuritis.