Can't offer a loan back outside of the transfer window- why?

[KingCanary]

I've got my eye on a 20 year old striker with 9 months left on his contract and want to beat the free agency rush by trying to buy him early. However I don't think he'll get much game time so my plan was to buy him but loan him back to Pescara where I'm signing him from. However this option is blacked out when I try and bid.

I understand you can't do loan deals outside of the window, but this would be a loan following the official date of the transfer which would be in the window. It seems odd that we can't make that agreement in advance?