"What Kieran has, firstly, is hugely underestimated," Southgate said after Trippier started in the win over Croatia at Euro 2020 on Sunday.
"I think people are still seeing the lad that was at Spurs a couple of years ago and not the defensive animal that has grown at Atletico Madrid, trusted by one of the best and most successful coaches in the world [Diego Simeone].
"He gets his distances right on cover, he's good one-v-one to stop crosses, and his talking is really good. We had a back four, there was always going to have changes in it on Sunday and we felt that communication, that organisation was an important part.
"We'll look at every opponent, we'll look at our team for every game. I think we have to have flexibility."