Johnson suffered concussion in the weekend draw at Blackburn and had to be taken off at half-time - much to his irritation.
Blues boss Alex McLeish insists he was right to replace the centre-back and is confident he will be able to count on Johnson for the game against freefalling Sunderland.
He said: "I had to drag Roger off. You know how he never wants to stop playing. He was just saying `give me half-time', but I said `no chance'.
"He had a bit of a rant and a rave, as he does. But I told him there was no way I was going to compromise the health and safety of one of my most important players.
"The doctor felt there was concussion. Roger was a bit groggy but he will get over it. We don't think it's too severe and hopefully he will get over it for the weekend."
Source: PA
Source: PA