I don't allow trades to be accepted during games. Some people may be more or less informed to injuries than others.
I'd nix the trade if I were the commish. Trading players of unequal value is one thing, at least they're playing.
Taking advantage of a trade that involves an injured player...well that's just a move by an ass...and I would seriously consider booting you out of my league.
Only 3 leagues this year. No sense in rooting for everyone in the NFL.