Challenge Cup holders Catalans Dragons are considering their place in the 2019 competition after being ordered to pay a £500,000 deposit to enter.
The French club became the first team from outside England to win rugby league's oldest trophy. Catalans have asked the Rugby Football League to "reconsider its demand", which applies to all non-English teams.
Owner Bernard Guasch said they want to defend the cup, but added "it would be irresponsible to accept" the decision. "The players would be very frustrated not being able to defend their title and we hope that we'll have an answer as soon as possible," Guasch said.
The deposit is understood to have been introduced to help cover any dip in revenue raised from the RFL's flagship competition.
While Catalans made history by winning in 2018, the final against Warrington was played in front of 50,672 - Wembley Stadium's lowest Challenge Cup final crowd since World War Two.
Already, fellow French club Toulouse and Canadian side Toronto - the first team from across the Atlantic to play in the Challenge Cup - have decided not to enter the competition. Both teams play in England's second division.
Red Star Belgrade, however, will remain in the competition and do not need to pay the bond as they are an amateur team that will play their opening two rounds away from home, should they progress.
The RFL confirmed issues about Catalans' cup defence were raised in December.
"We have been surprised and disappointed by the uncertainty over the Catalans Dragons participation in the 2019 Challenge Cup, which surfaced just before Christmas," a statement said.
"We have been in discussions with the club since then, and will continue those discussions to search for a solution."