The Super League matches between St Helens and Hull KR on Friday, and Catalans Dragons against Castleford Tigers have been postponed.
Both Saints and Castleford have more than seven players missing either through a positive test, or track and trace.
However, the game between Catalans and Hull KR, which was postponed earlier this month, will now be played on Saturday.
The RFL’s Chief Regulatory Officer Karen Moorhouse said: “The growing number of postponements, while reflecting the prevalence of Covid-19 in society, is a major concern for Rugby League as for other sports.
“In that context, Hull KR’s willingness to rearrange their away match against Catalans Dragons is an example of the flexibility that served the sport so well through 2020, and which may be required over the coming weeks and months.”