Alexander-Arnold scored in victory over Sunderland on Sunday.
“I thought Sunderland would be a test for him because (George) Honeyman is one of the best wingers in the U23 league. He's played in Sunderland's first team, he's a good player and I thought Trent would have more of a defensive role.
“But he never. He won that battle convincingly really, and when he went forward he was threatening every time.
“Speed, aggression, strength; he had it all. But I just want him to knock out 10 performances. He's had two or three, let's see if he can knock out 10 and go from there.
“The confidence of training with the first team on a regular basis, you can see the development he has made. Training at Melwood every day with top players, you can iron out mistakes and go to another level."