One of the factors to be considered is are we getting access to a player that we consider to be of such a level, that without this deal we wouldn’t be able to get? Therefore the reduction in upside (less profit) is outweighed by having an uplift in performance (compared to other options/ players we have).
I’m also assuming that such a deal would imply that we have confidence that he’s not going to bomb completely.
Of course, we are basically saying OK real talk we can't attract a future superstar but can take one off your hands to develop temporarily.
As convinced as we may be, and I do think he is a future star, there's no such thing as a sure thing.
For me the £10m upside off the back of what must be a significant chunk of our transfer budget isn't worth it. Part of this is also my own anxiety that this isn't how a' big club' acts and we are getting mugged off taking 30m of risk for someone else... But if we get to the last few days of the window I've no doubt I'd bite your arm off.
You'd struggle to convince me at any point however that £30m+ can't be better spent to turn over more than £10m of profit in today's market. I might get desperate enough to take the temporary talent, but I won't accept its a good deal.