Regarding de Villiers, Muir said: "Jean had very bad luck in that first game and we moved Frans [Steyn] into that position from fullback. What happened is typical of this wonderful game. You give a guy a gap and he takes it, and then the old incumbent has to fight his way back in.
"That does not means Jean will not be considered at all going forward, he will get a chance on Friday to show what he can do. He is a special player, he also has X-factor and he will get an opportunity to prove that."
Muir pointed out that Steyn's long-range kicking ability is an important element of the Springboks' arsenal.
"I am not aware of other kickers at the World Cup that can pot them from the distance that Frans does. That is part of his X-factor," Muir said. "We took a view a while back that a critical area of the World Cup would be the accuracy of kicking and we are blessed to have two super Steyns - Morne hardly ever misses and Frans kicks them from 50 metres-plus. Kicking is going to be key in these high pressure games, starting with Samoa, and if we get through that, in our quarter-final and beyond."
Muir said that the team was on Cup final footing as from this week.
"Every game from now on is a knock-out. Only the All Blacks have qualified for the quarter-finals. We have said to ourselves: 'if we don't win, we go home'. We are not thinking about the bonus point scenario [if the Boks get a bonus point they will be safe, win or lose]. This is it!"