They don’t hold up the initial trade for it…. But if a player comes in at next convenient time and goes through medical and they find something that wasn’t disclosed, then they explore having the trade reversed at that point, which can cause all kinds of problems for both teams if they have made other moves in the interim….Has happened a couple times in the past…. I’m trying to remember the last time it happened… it wasn’t thaaaaat long ago I don’t think, but my memory is failing me in my old age….