If he comes back and we have an injury crisis during the later rounds, everybody would castigate Moyes for letting him be cup tied, we don't need to do Leeds any favours.
Its not doing Leeds a favour its doing us a favour.
If we were playing Spurs in the cup people would say we can't play Barkley in this kind of game he's not ready, he might make a mistake and it would be better if we can send him on loan and make mistakes for them.
Well he won't learn a damn thing sitting on the bench all because by some freak chance we have no other players left due to injury that we have to play Barkley in later rounds.
The same Barkley who isn't ready to play for us but can't play for Leeds in case he needs to play for us. Makes no sense.
What he'd get out of a game like this far outweighs the chance that we'd be so desperate for players we'd recall a player who apparently isn't good enough to actually play for us.