Knights CEO Phil Gardner has confirmed a "substantial" number of players have tested positive to the coronavirus and been ordered to isolate at home.

Newcastle's players were set to travel by bus today to Tamworth, where they were to spend two weeks in camp at Farrer Agricultual High School.

That has now been scrapped.

Instead players who have tested negative will resume training on Thursday in Newcastle.

The Knights finished training ahead of schdule for their Christmas break, because of concerns about COVID.

There are now concerns about fitness levels, especially for the players in isolation.

Newcastle are scheduled to play their first pre-season trial in late February.

Gardner said his players had been "excellent" in trying to safeguard themselves against COVID but it was almost impossible to avoid, given their sheer volume of case numbers in Newcastle and NSW.