Johnson made his final public appearance on Monday morning before his 30-man party's flight to New Zealand later on Monday afternoon.
And the England manager was confident all of those carrying injuries would recover in time to train ahead of the Pool B clash with Argentina in just under two weeks' time.
Captain Lewis Moody, scrum-half Ben Youngs (both knee) and forwards Tom Wood and Nick Easter (both calf) all missed Saturday's final warm-up match in Ireland, while Mark Cueto suffered a back injury during the victory in Dublin.
But Johnson said: "We're pretty confident everyone will be fit to train in the Argentina week.
"Tom Wood and Nick Easter, with their injuries in particular, and Mark Cueto should be fine by the end of the week."
Yet, Johnson was under no illusions that injuries were bound to strike during what could be a near two-month stay in New Zealand.
"It's a fact of life going into any Test week," said Johnson.
"It just makes it more difficult - 30 players so far away. But we'll deal with that."
Johnson, who was forced to play some people slightly out of position on Saturday, added: "This is what World Cup week will be like because there are going to be late changes, potentially, and guys may have to fill in, as they did.
"Courtney (Lawes) played six, and Tom (Croft) played seven and James (Haskell) played eight, and did it pretty well."
Johnson is not afraid to do the same in New Zealand, saying: "We trust all 30 and they'll have to play at some point.
"We've got good choices. We can choose slightly different players in positions and go with what we think is appropriate.
"We'll just pick the team, as we always do, that we think's the right one to win the game."
Johnson, who captained England to World Cup glory in Australia eight years ago, added: "I know what World Cups are about.
"We've got to start with a really big game, which I think is good.
"We've got to be right there from the first whistle.
"In a busy international season, there are lots of games, but World Cups are very special.
"We're just doing everything we can to make sure we perform."
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