According to O'Neill, the trials and tribulations of the past few months can be the making of Johnson.
"I think it has been good for him to play here," said O'Neill.
"If he had stayed at City and played cameo roles, it might have given him a false feeling of where he is in his career.
"He is almost expected to win games single-handedly by some supporters. That's hard and he has to come to terms with all that."