Hypothetical question

We sign Luke Steele on loan for the rest of the season, agree to pay his wages and sign him for next year. We then go ahead and beat Cardiff to make the cup final against WBA. Obviously Steele can no longer play in the cup final due to him being on loan from WBA. We now need to sign in another keeper, however if memory serves me correctly the transfer window closes towards the end of March ( before the semi) so any extraordinary circumstances for a signing must be run through the bodies in charge of the game I.e the FA and the league.
Whats to stop the people in charge looking down our squad list and saying "why do you need to sign another keeper? You haven't put one on the bench for ages and you still have Letheran on your books, play him in the final"?

 

There wouldnt be much option other than to play Letheren

Cant let that get in the way of any deal for Steele though.

If that was to happen, then you have to play the cards you're dealt. What happens if Steele, or whoever signs, then gets injured next month?