Naming a 35-man squad for this month's friendlies, Tuchel ignored Real Madrid fullback Alexander-Arnold in a sign that the Scouser will miss this summer's World Cup.
Asked for his reaction, Gerrard said today: "Very much so, (I was surprised).
"Listen, we’ve got some good options at right back, Reece James is world class in my opinion, (Tino) Livramento - I know he’s had a couple of injuries, but he can play both sides.
"I understand the selection but I just think, is Trent Alexander-Arnold in the best 35 players in this country? Of course he is.
"And there are going to be certain games where England have to open the door, they might be against a low block, and it’s really frustrating. And Alexander-Arnold is one of these players who can come off the bench, and completely change the game with one pass. He’s that level of a player.
"So I am surprised, and disappointed for him."
Gerrard, however, added: "But there’s a lot of other circumstances to take into consideration - how much has he played?
"Is he physically in his best condition? Is there stuff going on off the pitch?
"Is it where (Tuchel) doesn’t want a group of players who are not going to be playing, or not in the first XI, who might be different people around the place? There’s a lot of things that might be taken into consideration before you select a squad for six weeks."