Former club Chelsea, who Johnson left to join Portsmouth, have been credited with making a bid, as have Manchester City and Liverpool, who in some reports are thought to be the front-runners for his signature.
Storrie admits he will not block the player from joining a club that will enable him to play in the UEFA Champions League next season.
He told Sky Sports News: "Glen has had a fantastic season for us and I think he is the best right-back in the country at the moment.
"I've know Glen a long while, from my West Ham days. When I re-signed him (at Portsmouth) we talked things over. He said, 'If one of the big four come in with Champions League football, would you stand in my way?'
"I told him I couldn't do that. Providing the deal is right for Portsmouth and Glen then we will look to try and do something in the right way.
"It is very hard to try and hold people back when they have a chance to play in the Champions League. I accept that."
When asked if an offer of between £15million and £18million had been tabled, Storrie replied: "You may not be a million miles away from the mark."
Storrie went on to concede that a deal could be struck imminently, adding: "I wouldn't think it would be too long."