Holt has struck three times this term - and has grabbed the equaliser in his team's previous two games.
Holt scored the injury-time penalty and Johnson said: "I see him do it every game in training.
"He has proved how important he is to this team. He has not been starting most games but like last week against Liverpool, he has come on and got the equalising goal.
"Holty could easily drop his head as he has not been playing but we cannot play both strikers because we play lone striker. But they both scored and they are fighting for that shirt."