The York squad will have to undertake a further round of COVID testing on Saturday morning for the 1895 Cup final to go ahead.
Although Featherstone have now been cleared following a full round of PCR testing on Thursday evening, York had one positive in their round of lateral flow testing.
As that follows two other positive results in previous days, the Multiple Cases Group require them to have a further round of testing on Saturday morning.
The 1895 Cup final is scheduled to be played before the Challenge Cup final between Castleford and St Helens on Saturday.
An RFL statement said: “Given the latest developments, any Featherstone or York supporters who do not wish to travel to the game can apply today (Friday) to have their tickets refunded, by contacting firstname.lastname@example.org .
“The results of York’s additional testing round will be confirmed as soon as possible on Saturday morning.”
Contingency plans, which would have involved the losing the semi-finalists possibly taking up a spot at Wembley, were only in force until Monday this week.
Featherstone beat Widnes to book their first Wembley date since their 1983 Challenge Cup final win over Hull, while York defeated Swinton.
Earlier this week, Featherstone reported a number of positive tests for COVID-19, which meant a full round of PCR testing was undertaken on Thursday night.
Though that was deemed a success, nothing was announced overnight and then the situation at York has since developed further.
It is due to be the second 1895 Cup final at Wembley, following Sheffield’s victory over Widnes in the inaugural event in 2019.
That game was played after the Challenge Cup final between Warrington and St Helens to a largely empty Wembley Stadium, other than a few thousand travelling fans from both Championship clubs.
The 2021 1895 Cup final is due to be broadcast via BBC Sport online and the red button.