Bookmakers Ladbrokes declined to extend their four-year deal after it ended with Catalans Dragons’ historic victory over Warrington at Wembley last August.
The Rugby Football League had lined up a replacement but it is thought a deal collapsed at the last minute and it has now begun the search for a new backer.
The draw for the first round, which will include Serbian representation for the first time in Red Star Belgrade, will be made in mid-December with matches due to take place on the weekend of January 26-27.
A new sponsor is unlikely to be in place by then but the RFL says it is prepared to bide its time in order to get the right deal.
Super League clubs are not due to enter the competition until the fifth-round stage in April.
An RFL spokesman said: “We have had strong interest, but having agreed a deal 10 weeks ago, that situation has changed in recent days - the situation remains commercially sensitive.
“We aren’t prepared to undervalue the Challenge Cup - it is an attractive property, the oldest knockout competition in rugby, with a special part in the history of Wembley Stadium, and generating substantial broadcast audiences through our relationship with the BBC.
“Our commercial team will continue to negotiate with potential partners, as the 2019 competition develops momentum through the early rounds until League One, Championship and Super League clubs enter in the spring.”
The RFL this week announced a new deal to keep the Cup final at Wembley until 2027 and unveiled a new competition, the 1895 Cup for Championship and League One clubs, to culminate at the national stadium on August 24, 2019.
As part of the new arrangement with Wembley, the Challenge Cup final will be brought forward to July from 2020.