NFL now saying 0 of the 171 players that had COVID have been diagnosed with myocarditis.

https://twitter.com/JohnKryk/status/1299400099332841473

Are they actually looking for it or do they just assume no one has it because no one has reported a problem yet?

There has been at least one confirmed case among MLB players[1]. It is also interesting to note that this cites a 10-20% number for the occurance of myocarditis among people with COVID-19.

[1] - https://www.espn.com/mlb/story/_/id/29579222/boston-red-sox-...

Your question is answered in the link GP posted. All were tested for it.

My bad. I read the link about the Big 10 which didn't mention anything about who was tested and didn't click through on the response about the NFL since it was a Twitter link and I assumed it wouldn't have any additional info.

What test did they do? Are these players that had a positive on a serology test or were they PCR confirmed cases?

This is really promising. I hope it holds up because if so, it has to mean there was some mistake or misunderstanding with the original report. (Well, or something malicious somewhere, but that doesn't make a lot sense to me since there's really nothing for anyone to gain.)

There was a mistake. Here is the clarification: https://twitter.com/BonaguraESPN/status/1301644428025540608?...

We have investigated ourselves and found that we have done nothing wrong.