I can't recall exactly, but I think it was after the Arsenal game.
I still think most of the first team should be risked in the Southampton game, since it actually might be the closest resemblance game to Ajax's we'll have, and they do still need to stretch their legs.
Valencia and Herrera need a long rest before the final IMO, they look very tired and single match rest isn't helping them. Risking Pogba when all our play depends on him is too risky but I can give him a game against South to be fresh, same for Rashford.