The Warriors boarded a private flight to the New South Wales town of Tamworth as the NRL plans to restart the coronavirus-hit 2020 season on May 28.
However, an "unwell" Roache was not on the flight from Auckland after contacting medical staff on Sunday morning.
Warriors centre David Fusitu'a also remained in New Zealand on compassionate grounds.
They're en route to Tamworth but David Fusitu'a and Nate Roache delayed.#ALLIN
— Vodafone Warriors (@NZWarriors) May 3, 2020
"Nate called the club first thing this morning saying he wasn't feeling well," Warriors chief executive Cameron George said in a statement.
"He was instructed to have a test immediately and was told not to report at the airport as he would not be travelling with the team.
"We're totally satisfied Nate has had no contact with any other player or staff member at the club for several weeks and we're very comfortable we have abided by all policies and requirements."
The Warriors departed New Zealand after finally being granted an exemption to travel to Australia on Saturday amid the COVID-19 pandemic.
The NRL season was postponed through just two rounds on March 23 and the league has been trying desperately to restart the competition.
Photo Getty Images Caption: Nathaniel Roache of New Zealand Warriors