Friday's Betfred Super League fixture between Leeds and St Helens has become the latest victim of the coronavirus pandemic.
Two Rhinos players have tested positive for Covid-19 in the last two days, forcing them to self-isolate for 10 days, and another seven have been shown to be close contacts through track and trace.
Under the Rugby Football League's Covid-19 protocols, a team can apply to postpone a match if seven or more senior players are unavailable and the governing body says it has accepted Leeds' request for the Headingley fixture.
It is blow for Leeds, who produced their best performance of the season to rout Castleford 60-6 in their last match a fortnight ago.
It is the second round-nine fixture to fall by the wayside after Huddersfield's scheduled home game against Wigan was postponed after seven Giants' players returned positive tests.
All four clubs will liaise with the RFL on possible re-arranged dates, although the table will again be determined by win points percentage to allow for the possibility of not all fixtures being fulfilled.
The Leeds game was due to be shown live by Sky Sports, who will now switch coverage to the match between Hull KR and Salford.
They are the first fixtures of the 2021 Super League season to fall victim to the pandemic, which caused havoc in 2020.
The Championship match between Halifax and Sheffield Eagles in May was postponed after two Eagles players returned positive tests and five more were forced to isolate under track and trace regulations.
Sunday's Women's Super League derby between St Helens and Wigan has been called off after a Saints players tested positive in the wake of Saturday's Challenge Cup final victory over York and more than five of her team-mates were ordered to self-isolate for 10 days.
Huddersfield and Leeds, who were both forced to close their training ground for five days in January due to a spate of positive tests, were inactive last week after being knocked out of the Challenge Cup and gave their players time off.