Soccer clubs go to extreme measures not to let opposing teams know if players are playing injured, or even if they may not play at all.
You know you opposition is in terms of the squad of players they can call from, so deal with all eventualities.
If a player is playing injured it should become apparent fairly soon. And if you avoid them and it doesn't, then you get what you deserve.
For the most part I like the rules of the NFL, but this strikes me as one of those rules that if it didn't exist and you suggested it people would be like:
There is nothing either good or bad, but thinking makes it so.