One assumes they'll need the money to cover their purchases? They'll likely use a short term loan to buy. Probably
@Beamrider can tell us?
Per their 2024 accounts they had bank facilities totalling £75m that they could draw on, of which £50m was drawn at the end of season 2023-24.
Over the previous three years they'd had injections of share capital just over £300m and a further £50m since their last set of accounts. So, basically put, they've been spending beyond their means and the PIF has been funding them. I imagine they would do so again if needed.
To put things into a wider perspective, most clubs have some term of revolving bank facility that they can draw down and repay as needed - football cashflow is quite lumpy through the season so clubs need to have, effectively, an overdraft to deal with the troughs. Newcastle's £75m is pretty low to be honest, I think they could quite easily secure more. However, it may be that the PIF has decided they would rather put the funding in themselves because it's cheaper - they'll have cash on hand, likely earning a lower return than the bank would charge Newcastle, so it makes sense for them to fund (this was the rationale for FSG lending us the funds to build the Main Stand).
It would certainly be easier for Newcastle to sell first and use those funds to buy but remember:
1. They only need to find 1/3 of the fees spent as deals are generally in three instalments.
2. They will probably be cash rich at present as they'll have just collected all their season ticket and seasonal hospitality money, plus some advance general admission ticket sales and sponsorship money for the coming season. Generally speaking, none of those payments would have come in before their previous year end, which is why their debt would have been largely drawn at that point.