Johnson is convinced he is ready to make his mark at the Stadium of Light.
He told Sky Sports News: "Fletch has proved himself this season. Without his goals, we would be in a lot worse position. He's going to be a big miss for us.
"I think it's important for the whole team to step up now and put the performances in we know we are capable of.
"It's important someone gets the goals with Fletch missing because we haven't scored that many or created many chances. When we get them, it's important to put them away.
"I think Danny is a couple of games away from getting a good run."