Johnson hopes the Robins can make ground on Cardiff, Swansea and Burnley, who are all involved in the FA Cup this weekend, while Sheffield United have no match.
He told the Evening Post: "It gives us a chance to put pressure on our rivals.
"Because the Championship is so competitive, you would always rather have points on the board than games in hand.
"Some of the teams around us are missing out this weekend and we have an opportunity to improve our position. If we can take the three points, those teams will be under greater pressure to win when they next play a Championship game."