The 22-year-old has impressed since joining Birmingham on a season-long loan from Manchester City last summer.
Johnson said: “The boys would welcome Joe on loan for another season, if not to sign permanently. Definitely.
“He is a good lad, nice to have around, works hard, plays well, so, yes, it would be a great signing for us.
“Hopefully it will happen. As long as we have got him (even if on loan again) that is the main thing.
“It is tough to find a keeper who does well week in and week out so I am pretty sure that will be the gaffer’s number one to sort out
“Joe is doing well and is keeping us in a few games. That is what he gets paid for and he has made some good saves in recent weeks.”
“Can he be England’s World Cup number one? Why not?” he added.
“If you look at all the statistics and records relating to keepers this season, Joe is top of them so there is no reason why not.
“Also, Fabio Capello is a manager who goes on form – so why not?”
