"It couldn't be worse news," says Glenn. "It has been confirmed this afternoon that it is a serious knee injury.
"We are not putting a time scale on when he will be fit to put on a West Ham shirt again, but he has ruptured his posterior cruciate ligament.
"It couldn't have come at a worse time, but it is much to early to say when he will be back.
"We are very very sorry for ourselves but we are deeply sorry for David himself.
"It was a freak injury, with his own player Martin Keown running into him, and it is one of those things I have got no control over, unfortunately.
"You are on a wing and a prayer with injuries, and the news is so disappointing.
"He didn't know the extent of the damage this morning and he was cheerful as you could be under the circumstance, but the scan has revealed John Green's worst fears."
The bitter irony of losing the services of his biggest summer signing has not been lost on Glenn, who says: "I think everyone was pleased with the signing and they should be because I felt I had signed a goalkeeper who, on his day, is as good as anyone in the country.
"It made a statement about what I was trying to do, the kind of quality I was looking to bring in.
"I am still looking to sign three or four players of David's quality, and we really need them now."
Glenn could not say whether David could get back playing in time for the World Cup next summer, adding: "It's much too early to say; he will be disappointed about that but his biggest concern is when he will put on a West Ham shirt again."
The blow to Glenn's plans in England's friendly against Holland just three days before the season starts does beg the question of whether the game should have been played at all, and Glenn says: "If there had been no injuries and we had all got away with it nothing would have been said.
"Although you have to say some high profile managers did voice their concern.
"But it's us that have been caught with the player who has a bad injury
"It was a fixture that wouldn't, in my opinion, have made any difference to the performance or the result of the Germany game.
"I can see the point of having a get-together, two or three days training, and working on certain things on the training ground.
"But I wasn't personally convinced the game was a real necessity.
"I'm not condemning them having the game; they certainly wouldn't have wanted anyone injured.
"But there you are; it's done and we have to pick ourselves up for a very important game on Saturday."
Shaka Hislop will take David's place in goal, with Steve Bywater being recalled early from his three month loan spell.
"It gives Shaka now the opportunity to go back into the team," says Glenn.
"Shaka will probably be the first to admit that last season was not his best whereas in the previous two seasons he did particularly well.
"We want Shaka back to the sort of form he was in two seasons ago - and he will get the opportunity to show that against Liverpool.
"Shaka is the sort of person who will be very upset by what has happened to David James; he is not one to think otherwise."
And, explaining why Steve has been recalled, he says: "I need to have three goalkeepers around the place and Steve will be back for training on Friday.
"Everyone was so disappointed this morning because of the fears for David's health.
"When they find out these results I don't suppose it will make them feel any better.
"But we have a short space of time to pick them up on Friday and get ourselves up to Liverpool.
"We're looking for the sort of performance and result that will give us a big lift."