We propose the use of the 1-minute sit-to-stand test (1STST) to evaluate the physical capacity and exertional desaturation one month after discharge in a sample of patients who survived COVID-19 pneumonia. This was a cross-sectional study that collected routine data from consecutive patients admitted to the outpatient program in a public hospital in Chile. Patients were asked to complete a 1STST. Data were analyzed according to those with and without a prolonged hospital stay of >10 days. Eighty-three percent of the patients were able to complete the test (N = 50). The median age was 62.7 ± 12.5 years. The average number of repetitions in the 1STST was 20.9 ± 4.8. Thirty-two percent of patients had a decrease in pulse oxygen saturation (SpO₂) ≥ 4 points. The prolonged hospital stay subgroup had a significant increase in exertional desaturation (mean difference = 2.6; 95% CI = 1.2 to 3.9; p = 0.001) and dyspnea (mean difference = 1.1; 95% CI = 0.4 to 2.1; p = 0.042) compared to the group of length of stay ≤10 days. In-hospital survivors of COVID-19, the 1STST showed a decrease in physical capacity at one month in those 90% who were able to complete it. The 1STST was able to discriminate between those with and without a prolonged hospital stay and was able to detect exertional desaturation in some patients.