"It is really sad news and no one is more disappointed than Michael himself," says Glenn.
"He has had two disappointments of late, because we all felt he had done enough to squeeze into the final 23 for the World Cup, but I have sat him down, had a chat with him, and told him there are three World Cups still for him to play in.
"I think he accepts that, though he still would have liked to have gone with Joe."
Michael has been replaced in the England under-21 squad by Jonathan Greening of Middlesbrough, who links up with the players in time for the opening game against Switzerland in Zurich on Friday, and Glenn adds: "He did have the safety net of the under-21s and now that has been taken away from him, but again he has got to accept he has to do what is right for his own body to make sure he is fully recovered for next year.
"He could, and perhaps should, have come off at half time on Saturday, but it wouldn't have saved him for the under-21s.
"I probably took a bit of a liberty leaving him on as long as I did, but such is the way things are you always want to win games and at 1-0 we needed that second goal so when we got it I took him straight off although there were only a couple of minutes left.
"When they equalised I persevered with Michael even though I knew he was starting to struggle, but it certainly won't make any difference for July 4th when we all come back."
Glenn thinks his upward curve will continue apace next season and adds: "Michael Carrick will just get better and better in the next seven or eight seasons, as will all the young players like Jermain and Joe - and, to be honest, I think a lot of players this year have had a better season this than last."
But Glenn also believes the more senior figures in the squad have improved this season, hence the Hammers' success, and he adds: "Trevor Sinclair has now forced his way into the World Cup 23, albeit unfortunately on the back of some dreadful news for Keiron Dyer and Steve Gerrard.
"Both boys are not officially out of the squad yet but they look very doubtful, and if Trevor does go into the World Cup it is on the back of a fantastic season.
"I know he had injuries the season before but he has proved such an important player for us this season.
"Christian Dailly is a great example. He has been the model of consistency this season after a very difficult start to his West Ham career last year.
"He has certainly won the fans over and, though this is not official, I have been told that he is probably going to be Scotland's captain on their far east tour this summer.
"He has been so consistent. It was a bit of a rocky start for all of us at the start of the season but since the Everton game and teaming up with Tomas Repka it has helped his own game.
"Most of them have had a better campaign - Fredi Kanoute is another example. Some of his finishes this year have been excellent and he is getting better and better."