Wales have sent home West Brom's Hal Robson-Kanu, Leeds striker Tyler Roberts and Stoke loanee Rabbi Matondo from their squad for breaching team protocols.
Although no details have been given by the Football Association of Wales, Roberts apologised on social media for breaking curfew - although he has since deleted the post.
"Gutted to be leaving the camp early, but rules are rules and I shouldn't have been up in the hotel later than the set time," he wrote.
Euro 2020
'An insensitive question' - Page backs Bale over interview walk-off after Wales defeat
26/06/2021 AT 20:40
Sorry to the team, staff and Wales fans. I will continue to work as hard as I can to earn my place in the squad for the Euros.
A statement from the FAW said: "The three players will be returning to their respective clubs this afternoon. The FAW will not be making any further comment."
Meanwhile, Gareth Bale has admitted the current World Cup qualifying campaign may be his final one. If the captain can guide his country to the tournament, he will be 33 by the time it starts in Qatar next year.
"Obviously, there's no hiding we are getting older and possibly it is the last campaign", he said.
"If it is, then it won't change my mindset. I'm going to be 100 per cent committed like always. We still have a big tournament to play in the summer and then continue with these qualifiers after.
"I'm purely focused on the present and what is happening now. Whatever will happen in the future will happen."
Wales lost 3-1 in their first qualifier against Belgium last week but beat Mexico in a friendly over the weekend. They play group leaders Czech Republic in Cardiff on Tuesday.
Euro 2020
Danish victory over Wales a tribute to towering team spirit
26/06/2021 AT 18:06
Euro 2020
Denmark smash four past Wales to keep dream alive
26/06/2021 AT 15:02