Foden and Greenwood, who is celebrating his 18th birthday today, have been omitted after their misdemeanour in Iceland last month, where they were fined by local police for breaching Covid-19 regulations having just made their senior debuts.
They were sent home, missing the game against Denmark, and Southgate has opted not to select them in a 30-man squad for the three games over the course of the next fortnight.
The manager has, however, said they will be available for selection for the games in November.
Southgate said: “Whatever decision we would have taken this would have been the story tomorrow.
“We have to send a message to all our players in our teams at every age level that that sort of thing isn’t how we do things with England.
“Then we’ve got to rehabilitate these two boys. Young people will make mistakes. These lads have suffered enough now.
“I think they need this period of reflection but that gives them the opportunity to get back on their feet with their clubs, enjoy their football again.
“I can speak to them after this camp and it will be just be about their form then.”
We have to send a message to all our players in our teams at every age level that that sort of thing isn’t how we do things with England
Manchester United boss Ole Gunnar Solskjaer publicly criticised Southgate’s decision to call-up Greenwood up last month and was even unhappier that he was put up before the media ahead of the Iceland game.
Southgate has since calmed the waters with Solksjaer but stands by his decision to pick the teenager.
“I have spoken to Ole, I felt that was important because the best way for us to communicate is always directly,” Southgate said. “We had a good chat last week, we are on a similar page on a lot of things.
“The only thing where there was a misunderstanding was that we did have contact from the club on all of their players, they were still in Europe, whether there would be this dispensation for clubs still in Europe. But there were four other clubs in that position.
“We didn’t get an individual request regarding Mason, we have talked it through, we are very much on the same page, we want to look after the young players.”
While Foden and Greenwood are absent, Harry Maguire is back involved after he missed September’s games.
The Manchester United captain was dropped from Southgate’s squad after he was found guilty of assaulting a police officer, swearing, resisting arrest and bribery following an alleged incident on Mykonos.
He subsequently appealed the verdict and his 21-month suspended prison sentence and Southgate never considered not bringing him back.
“I think I said last month there was absolutely no reason we couldn’t pick Harry this time,” he said.
“He has been our most reliable defender over the last couple of years so it was not even a consideration that he would be in the squad or not.”