Croatia boss Zlatko Dalic claimed his side had paid the price for their exertions in Thursday's win against Spain, as they lost their 1-0 lead to concede two late goals to be relegated from their group.
"It was very difficult for us to recover after the match against Spain. We don't have such a big squad," he said.
"In the last 15 minutes we lost concentration, which could be down to our condition physically."
Referencing a popular England fans' song, Dalic backed Southgate's team to fulfil their potential soon.
"They have a young and fast team. It's coming home, very soon!," he said.