The Harlequins No.8 was a late withdrawal from the side that beat Georgia 41-10 after he suffered a back injury - with Easter having been forced to sit out training.
Thomas Waldrom has already arrived in New Zealand as cover should Easter fail to recover.
Johnson has admitted that Easter was "progressing" but a final call would be made ahead of England's move to Auckland, where they will begin preparations for their decisive showdown with Scotland.
"Nick's progressing. We'll see where we are after Saturday," said Johnson.
"Nick's not had this injury before, it's just one of those where we're hoping he's going to be good to go next week.
"All the signs are he will be. It looks good but these things are day to day. We've got to (make a decision) after the game.
"He'd be a loss. That's why we had guys in through the camp. Thomas was in learning what we do, so if the situation arises he can put himself in contention pretty quickly.
"I think Nick will be okay. He's desperate to get back and play but we'll see how it progresses over the next 48 hours."
James Haskell will continue at No.8 in Easter's absence, having also successfully deputised for Lewis Moody at openside in England's tournament-opening victory over Argentina.
And Haskell's form means there is no guarantee Easter would come straight back into the team to play Scotland, even if he was fully fit.
"(Haskell) came in last week for us at short notice and he's done very well," Johnson said. "He's keen to improve and when he's been in the team, he's often covering multiple positions depending on who we have on the bench.
"At times he's covered all three, so he has to know all those roles and he's done a good job of it - he's playing well and he's a useful player to have with his utility."
England are still to replace injured prop Andrew Sheridan in their squad, with Johnson preferring to continue with a 29-man squad and keep his options open.
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