Right-back Alexander-Arnold completed the full 90 minutes for the first time following a knee injury that sidelined him for four weeks in Tuesday’s Champions League clash with Bayern Munich.
Starting with this afternoon’s fixture, Liverpool face a period of three games in seven days - leading Klopp to name Alexander-Arnold on the bench at Old Trafford.
“Just because Trent was out for a while, played the last game and we have two games coming up,” the manager said, when asked to explain his starting line-up.
“I don’t like to think too much about the games coming up usually, but it’s pretty much the first moment in the season for while that we could make a decision with Millie and we will need Trent in the next weeks very much.