There have been 10 positive Covid-19 tests across five clubs in the latest round of Super League testing.
Both Castleford and Wigan have confirmed positive results for three players, while Wakefield and Hull FC have each seen one player return a positive test.
The Tigers stood down from their scheduled game at Leeds on Thursday, to be replaced by Hull FC.
All eight players and two non-playing staff members are now self-isolating.
Meanwhile, Wakefield chairman Michael Carter has revealed that the club have been forced to stand down eight players through track and trace and have just 14 fit players to select from for their match against St Helens on Friday.
Carter said that the remaining three places in the 17-man squad would be made up of the "least injured" players.
"If Cas hadn't have been in the position they were in yesterday, we'd have been the ones to ask Hull to play Saints on Friday and we'll pick up a fixture the week after," he said.
"But if you go in chronological order, Cas have had their issues first and got that switch and we have nowhere to go."
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