Background Because of the high injury rate currently seen in soccer players and the exceptional pandemic circumstances, the question arises to what extent this reported increase in injury incidence is associated with COVID-19.

Objectives The aim of this study was to investigate the association between COVID-19 and muscle strain injury occurrence in elite athletes.

Design A prospective cohort study

Setting During the first half of the 2020–2021 season, injury data was collected by using the UEFA injury card. Assessment of SARS-CoV-2 infection was performed by means of a polymerase chain reaction (PCR) test before each official game.

Patients (or Participants) Three Belgian professional male soccer teams (84 players in total) participated.

Interventions (or Assessment of Risk Factors) Regression analysis was performed to identify the risk of developing a muscle strain injury after SARS-CoV-2 infection.

Main Outcome Measurements Muscle strain injury, COVID-19 diagnosis, quarantine duration.

Results Eighteen players developed a muscle strain injury during the study period (June 2020- January 2021), of which 11 players were diagnosed with COVID-19. Regression analysis showed a significant association between SARS-CoV-2 infection and the development of muscle strain injuries (p=0.010). The athletes that developed a muscle strain injury after COVID-19 diagnosis were all injured within the first month (15.71 ± 11.74 days) after sports resumption and showed a longer quarantine duration (14.57 ± 6.50 days) compared to the SARS-CoV-2 infected players that did not develop a muscle strain injury (11.18 ± 5.25 days).

Conclusion This study demonstrated a five-time higher risk to develop a muscle strain injury after a SARS-CoV-2 infection in elite soccer players. Although this should be examined further, it seems possible that short-term detraining effects due to quarantine are associated with a higher risk of muscle strain injury and could possibly be related to lower physical readiness and higher rates of fatigue.