As Fredi looks to return to action in the reserves on Tuesday night after a frustrating lay off, John says: "It goes without saying he has been demoralised by the injury.
"But we feel he is being strengthened and if he has a good run now he will be able to build his fitness up and it shouldn't be a problem.
"It was a freak episode at Chelsea, like stepping on a very large banana skin and with his manner of play it wasn't helpful to say the least.
"He didn't get that injury because he was weak. He was very unlucky as it was just the way of movement and the piece of play that he was involved in.
"We felt it was an unusual movement that could have happened to any player."
Fredi, who missed half of last season through a hamstring problem, is hoping to put his problems behind him now - and John is hopeful he can.
"No one can ever predict," he says, "but Fredi is resolved towards working hard in the gym and he is in before most people doing his own work - as are a couple of other players as well.
"He will stay on to do work after training too, so he does apply himself very well - so let's hope that diligence pays off."