The Kiwi NRL club has advised long-serving playmaker Johnson to test his value on the open market, even though there's a year to run on his contract.
The timing and public nature of the Warriors announcement was criticised by Nikorima, coming midway through New Zealand's three-Test series in England.
He said his room mate Johnson was caught off guard, days out from Sunday's second Test in Liverpool.
"I've spoken to Shaun about it. I thought it was pretty harsh the way it all came out and him being on the other side of the world, not having any control over that," Nikorima said.
"I just told him, 'Stay focused, you're part of this team now and the rest will just take care of itself'."
The most influential player at the Warriors since his debut in 2011, Johnson is reportedly in Canberra's sights.
The Raiders are believed to have requested the 28-year-old cut his contract short and cross the Tasman as soon as next season to resolve a shortage of options in the halves.
Nikorima didn't think the uncertainty surrounding his teammate would prove a distraction as the tourists seek to reverse last week's 18-16 loss in Hull.
"He doesn't show too much and he's still the same Shaun Johnson that first came over here before all that came out," Nikorima said.
The Broncos playmaker believes his combination with Johnson has taken great strides since last year's failed World Cup campaign.
The pair impressed in last month's upset of the Kangaroos and aren't as restricted in their roles under Michael Maguire as when they oversaw a stuttering attack in the quarter-final loss to Fiji.
"If you look back at the World Cup, we both stuck to one side. Instead of now, we're roaming," he said.
"I think we're getting a really good combo happening. We haven't played that much games (together) but the fact that we're room mates now helps out a little bit - getting to know each other's personalities.
"I'm a bit of a clown and he's the more serious one."