Our league allows one player to be placed on the IR if they are listed as Questionable, Doubtful or Out. If that player's status is upgraded to Probable or declared healthy then the owner must immediately take him off of the IR. If the Owner does not have another player to put on IR then he must IMMEDIATELY drop a player to keep his roster at the legal limit. There is no time granted to that owner to try and work out trades or anything of that nature. An owner can not start a player that is on his IR.
That's my two cents and it's worth every penny of it!