the club is only with what someone works party for it and it's assets. the playing staff and physical assets have a value on the balance sheet. income via the premier league and their media deals is not an asset, but factors into the value. realistically, the only way he increases the value of the club is by increasing the value of the assets. the new stadium does that, as does increasing the value of the playing squad through recruitment, coaching, or bringing through youth players.
it's essentially the same as your house - it has a paper value, but you can only release the value through a sale or through equity release via a loan against the perceived value. if you increase the value then you can loan against the increased perceived value similar to what man utd did, but first he has to increase the value.
in other words, he's going nowhere unless he decides to sell at a loss, and the new stadium is arguably his best way to get *anything* back on his investment.