It was certainly unwise of Ancelotti to field all of his attacking stars against Barca, as the inclusion of Mbappe, Bellingham, Vinicius and Rodrygo left Federico Valverde and Eduardo Camavinga with too much work to do, and the latter was utterly overwhelmed during what was probably his worst ever performance in a Madrid shirt.
Left-back Ferland Mendy, meanwhile, wasn't much better than Vazquez on the opposite side of the defence, and even the usually dependable Antonio Rudiger cut a desperately frustrated figure as he lashed out at the likes of Lamine Yamal. In such circumstances, throwing Alexander-Arnold or even the equally attack-minded Alphonso Davies into the mix during the January transfer window would hardly help matters much (even if such deals were possible, which seems like wishful thinking at the moment).
Certainly, bringing in a proper right-back would at least mean not having to ask Valverde, Madrid's best midfielder, to fill in there, but there's no denying that Alexander-Arnold is far better going forwards than backwards, so it's not as if opponents would suddenly stop trying to attack Real down the left even if Liverpool could be persuaded to part company with their homegrown hero in the middle of a Premier League title push. The reality of the situation is that Ancelotti has far greater need of a player capable of restoring order in the middle of the pitch, given neither Tchouameni nor Camavinga appear up to the task.
Above all else, though, Madrid are crying out for a dominant central defender - and it doesn't look like they're going to get one before the end of the month, meaning Ancelotti's best bet is dropping one of his forwards to the bench in order to make room for an extra body in midfield to give greater protection to his "fragile" back four.
Luka Modric correctly pointed out that Madrid are at least lucky that Sunday's embarrassing defeat didn't come in a more meaningful match, but the significance of the shocking showing in Saudi Arabia cannot be downplayed. Despite claiming that they had carried out a "clear" and comprehensive review, Ancelotti & Co. clearly didn't learn any lessons from October's loss to Barca, and if they don't act after this second consecutive Clasico capitulation, Madrid will endure even more miserable defeats before the season is out. Right now, in fact, any top team in Europe would fancy their chances against a side with such a soft centre.
Alexander-Arnold would be well advised, then, to bide his time before putting pen to paper on any deal with Madrid. Unless the centre of defence is strengthened, he'd be more exposed at the Bernabeu than he's ever been at Anfield.