The Australian was on Tuesday set to announce his team to face England in the tournament opener at Twickenham on Saturday.
His predecessor Andy Robinson led the side to the wooden spoon following five straight defeats in last year's competition before resigning after a humiliating 21-15 loss to Tonga in the autumn internationals.
But Johnson was adamant pre-match speculating over the Scots' chances of success this time round was a pointless exercise.
He said: "Everyone keeps asking me to say what I think a successful tournament will be but I'm not going to do it because I don't believe in it.
"I know what everyone wants. And trust me, I'm the most competitive bloke in the world. I would wrestle with you for marbles.
"The reality is, for us to get the [wins] regularly, we need to get performances. We need to understand what we are. And if we get incremental improvements all the time, then the [wins] will take care of themselves.
"It's about deeds. Let's stop talking about it. I can't sit here and tell you [how we will fare] and nor will I."
Johnson has already trimmed a 35-man training squad down to a group of 27 this week. Today he will break the bad news to four other unlucky candidates who have failed to make it into the 23-man squad heading to London.
Certain to be among the starting XV will be skipper Kelly Brown - whose captaincy was confirmed on Monday - but Johnson admits there have been other names which have taken longer to deliberate over.
And he hinted that he may be ready to give his starting selection are more youthful look.
He said: "There has been competition in a couple of places but we are honest about the situation here. We don't have the depth of player pool that other nations have.
"But rather than wallowing in that, we have acknowledged that. There was some good competition. There were three or four that we discussed heavily but the rest we were happy with a week or so ago.
"We kept an eye on form of the players but also the future for this country. We have a competition to compete in so I'm not being negligent of my duties as we are going to a pretty hostile place this weekend.
"But there have been decisions made that have not just been for this Test. We have to keep an eye on the future so we can get some mileage on the clock."
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