The winger was not selected as part of Southgate’s squad for Euro 2024 in Germany.
While Grealish was a part of the initial 33-man training group, he failed to make the final list.
Harry Maguire, James Maddison, Jarrel Quansah, James Trafford, Jarrad Branthwaite and Curtis Jones were also axed.
England boss Southgate said: “I think you put yourself in the shoes of a player. You put yourself in the shoes of a parent. You understand that for these players this is a devastating moment. It can be career changing for those who are going.
“So you give the decision making process all the attention it deserves and then you try and deliver it as humanly as possible. Then you have accept the person receiving could take it in any number of ways. I have to say all of them were really respectful.
“I tried to tell them all as early as I could. I knew exactly last night where we were with James and didn’t want him to be hanging on and training when I knew I could tell him.
“I couldn’t do that with Jack until this morning because there might have been someone else who might not have come through.
“Look, I think every player knew there was a certain amount of jeopardy if I’m frank. The younger ones, we’d had some of those conversations before they arrived – that this is the likely plan but come in, have the experience. So for them it was different.
“For some of the others they’ve been with us a long time, big characters within the group and clearly when you’ve worked with guys for a while you know there’s a different dynamic to it, different level of expectation, different relationship between us.
“And you accept that can be damaged short term or long term. And I understand that but I have to make strong decisions. I’ve never backed away from that and I never will.”