England manager Gareth Southgate said Mason Mount and Ben Chilwell's absence from the 1-0 win over the Czech Republic in Euro 2020 was "bizarre" after they had to self-isolate as close contacts of Scotland's Billy Gilmour.
England said before Tuesday's match that the entire squad and staff returned negative Covid-19 results but Mount and Chilwell would have to isolate until June 28 after coming into contact with Chelsea teammate Gilmour.
Mount and Chilwell were pictured embracing Gilmour at the end of last weekend's goalless draw.
None of the Scotland players had to isolate after Gilmour's positive test on Monday.
"Frankly I don't understand it at all," Southgate said. "There are teams travelling around by plane, coach, bus in enclosed spaces for hours.
"It's hugely disappointing for the players. It's a bizarre situation really. They've spent 120 seconds too long in a fairly open space.
"It's full of contradictions for me but we have to get on with it."
Southgate believes there is "more to come" from England after they ensured a tough-looking Wembley return in the last-16 by beating the Czech Republic.
Raheem Sterling headed home impressive Jack Grealish's cross to seal a 1-0 victory as already-qualified England progressed as Group D winners.
The reward is a Wembley return next Tuesday against France, Germany, Portugal or Hungary - a big jump in quality after progressing unbeaten and without conceding.
"We've played two opponents in the Croats and the Czechs who I think are playing at a very good level," Southgate said after setting up the last-16 tie against the runners-up in the so-called 'Group of Death'.
"And Scotland, which as an occasion and an experience for our players, especially the younger ones, was a quite unique and really important one, so these will be different games.
"We know world champions, European champions and Germany, who to me look like they're back on song. They've brought some very experienced players back in.
"So whoever we play, [will be a] really, really tough opposition but we've sort of known that for 18 months. We've known the route through.
"The good thing from our point of view is I think we're still improving, we look difficult to play against. There's more to come from us.
"We've got more match minutes on the pitch for some important players and that squad depth is going to be important because I felt like we've run out of steam a little bit in a couple of the games.
"To be able to make the changes and the substitutions has been really helpful to manage the games."
The side has plenty to work on ahead of next week's knockout clash, though there are also positives to take from the Group D decider.
Harry Maguire put in an encouraging performance as he returned from a six-week lay-off with an ankle injury, while Jordan Henderson played another 45 minutes after undergoing groin surgery in February.
Playmaker Grealish looked sharp as he started his first major tournament match, while 19-year-old Bukayo Saka produced a man-of-the-match display as he stepped out on this stage for the first time.
"Jack produced a fabulous cross for the goal," said Southgate.
"We saw some of the interchange of positions of those forward players was really exciting, I thought at the start of the game especially. We tired a little bit but we knew that because one or two are a little bit short of fitness.
"Bukayo, I can't speak highly enough of him. He's earned that opportunity.
"His performances in training since he's joined this camp have been outstanding.
"He played well in the game at the Riverside. We've talked about playing him in some of the previous matches and, yeah, he earned that chance tonight and he's grabbed it. He was fabulous."
