4-player defense seem worked, but Trent was meh. He's ass in the last two games, and bad defensively. Xabi must tell him about flaws. Although he's older than Huijsen, but his performance is not as good as Huijsen.
Trent has speed and when in counter-attack mode he is very good at piercing the right side of the opponent's defense, this is one of his advantages and that's why Real Madrid wants him but his weakness when in defense he is not strong enough sometimes he loses his position and is not consistent enough in defensive transitions but I think Xabi can overcome this weakness and one example is implementing 4 defenders as a cover to cover his shortcomings, in 2 matches Xabi has not been successful enough but I am sure that over time and the chemistry between Trent and his defense partners is well established this will work.