Sven-Goran Eriksson watched Joe against Manchester United recently, and in the aftermath of that game one senior journalist wrote an opinion piece saying he would not go to the World Cup.
But he has, of course been picked for the squad to face Italy at Elland Road on Wednesday and Glenn says: "Critics speak their mind and hopefully they do it as an honest opinion, but Joe has still got huge potential.
"As I have always said, no young player has come into the game of professional football under such a barrage of hype, which made life very difficult for him.
"I am very conscious of going the other way with our young players because there is enough pressure on them without the added pressure of all the media attention, so I try to be low key with them and think in the long run that will hopefully pay off in what are going to be long successful careers.
"But as far as Joe is concerned that had already gone before him. It just makes it that much more difficult for him to have to play under that pressure.
"But I think overall he is coming along fine - he has added a few more strings to his bow this year. There are things he has done in games in midfield from a defensive point of view that no one thought he could do.
"Eventually he will come out of it a more complete midfield player.
"He definitely always showed us in training that he could do those things. There is a long way to go and we need to keep working hard with him on all aspects of his game and encouraging him - at 20 he can only get better."
Joe is accompanied by David James and Trevor Sinclair in the full England selection, while Michael Carrick, just back from injury, sits it out - for the time being.
Adds Glenn: "I am very pleased, delighted, to see the boys get a call up, just as I was to see others get in for their countries like Steve Lomas, Grant McCann, Vladimir Labant, and of course Jermain Defoe for the under 21s.
"I knew that Michael would be held back in view of the fact that he has only played one game since the hernia operation which made sense, really.
"But I am sure that Michael will force his way back into the squad by the end of April for the game against Paraguay.
"He is a quality player and I'm sure there is enough time in the next month when we have got six games in which he can give himself a decent chance to get into that final squad."
He is full of praise for Michael and Steve Lomas making comeback appearances against Manchester United - and hopes, with Don Hutchison out long term, there are no more nasty surprises in store for him this season.
"It was an extremely tough game for Michael and Steve but you could argue that those two were the best players on the day - I thought Michael had an excellent game, as did Steve.
"We need everyone back who is available. Obviously Don is out until September at the earliest and with the smallness of the squad we need to keep everyone fit, crack on, and get all the points we can get as soon as we can."