Former England and Everton goalkeeper Nigel Martyn has fears for the country's keeper stocks.
He told the Mirror: "The thing that astounds me with Hart is that he has not made more mistakes at his age. He will make mistakes [and] will get slaughtered, but has the confidence to just shrug it off.
"It really helps that he's at a top club. This is the first time that we've had an England keeper at that level since Dave Seaman retired.
"He also exudes confidence. He gives his defenders confidence that he's there for crosses and to save shots when called upon. He can be a top, top keeper.
"Beyond that, it's hard to see too much quality. I was at Leeds at the same time as Scott Carson and he has developed a habit of making too many mistakes.
"[Newcastle's] Fraser Forster has done well [on loan] at Celtic. He is under pressure under every game but has handled it well. I've also seen [Watford's] Scott Loach up close and he's working hard at his game.
"But you always need strength in depth, good cover and good people pushing each other. That's why it's such a shame that Green and Foster have taken their decisions."