"It's not a gamble. You always put a lot of thought into your selections, no more so than when you're in a World Cup quarter-final," Johnson said.
"It's one of the options we've got. I think Mike and Manu [Tuilagi] have played well together. If we had to play Shontayne; there's always an argument to play him.
"It does give us some different things that we can do on the field when we play [Flood and Wilkinson]."
England face France on Saturday, with the game starting 8.30am UK time.