Nunez looked to pull his hamstring in the 17th minute of Saturday’s 1-1 home draw with Leicester City but wasn’t subbed off until the 85th minute.
Having been left out of tonight’s squad, McKenna revealed: “It’s a hamstring injury that he picked up in the game on Saturday.
“So it no for this one, it’s no for Saturday (at Sheffield Wednesday) and probably no for the one after that (Millwall at home) as well.”
Meanwhile, midfielder Azor Matusiwa was subbed in the latter stages of this game.
“Yeah, he’s struggling with his hamstring too,” said McKenna. “It’s too early to say how bad that is.”