You'll see the team doctors do the "ACL test", where they straighten their leg and have the hand under/cupping the knee and basically pull it straight. It's not foolproof but it's probably about 95% accurate, sadly from my personal experience it was 100% accurate
Generally the only time it's wrong is if there is catastrophic damage where you can't differentiate what's busted and the ones with only a minor tear that ends up being enough that you need the surgery still, the partial rupture (someone like Kawhi Leonard is an example of these, no idea how his test went though obviously).