Les Bleus only just reached the knockout stages of the tournament after two wins and two defeats in Pool A, including a shock defeat to Tonga on Saturday.
Despite their typically indifferent form, Johnson believes that they still have the potential to derail England's World Cup campaign.
"France losing to Tonga means nothing," he said. "You play these games in isolation.
"When you get to a quarter-final, what happened last week, last month, last year or the last time we played them means nothing.
"France are dangerous and never more so than when flying under the radar a bit, which they are, but so are we. It steps up next week in terms of the opposition."
The last time the two sides met was in this year's Six Nations competition, which England won 17-9.