This isn't something that's likely to ever be verified conclusively, but we do have evidence that COVID-19 is associated with myocardial injury and myocarditis. Sure, it's not impossible a young, fit and healthy professional athlete was suffering from undiagnosed heart inflammation prior to contracting a novel virus. It's very unlikely to be the case when a bunch of healthy young people are suddenly diagnosed with the condition concurrent to testing positive for COVID-19, though.

https://www.msn.com/en-us/sports/more-sports/what-e2-80-99s-...

https://www.sciencedirect.com/science/article/pii/S2589790X2...