Ryan Farquhar and Jeremy McWilliams have both had late entries for this weekend's Sunflower Trophy turned down by the meeting's organisers.
Farquhar, who retired from the sport last season, was considering a racing comeback at the Bishopscourt event.
Dungannon man Farquhar was told by organisers the start list was full and that he was too late entering his team.
Former MotoGP rider McWilliams, 49, won the Supertwins event for Farquhar's KMR team at this year's North West 200.
"I was considering going out at the Sunflower, just for a run-out, not to be competitive but just to help develop the bike," said Farquhar.
"I spoke to the organisers but they came back to me and said there was no room for me, which I am very disappointed about. No KMR bikes will be out at it.
"There are quite a few spectators who would have been glad to see us ride."
The Sunflower club told BBC Sport that there had been 50 entries for a 35-place grid and that McWilliams had been unable to participate in Friday's qualifying session.
But while the veteran riders have been ruled out of Saturday's meeting, the entries do include British Supersport Championship rivals Stuart Easton and Alastair Seeley plus PJ Jacobsen and Ben Wilson.
Gearlink Kawasaki rider Seeley will take part in the Superbike and Supersport classes, as will his British Supersport rival Easton, aboard Mar-Train Yamahas.
American Tyco TAS Suzuki star Jacobsen will join them for the Superbike races.
Wilson will be a leading contender for the keenly anticipated 600cc events.
The end-of-season meeting is back on the calendar after a year's absence and will again incorporate the final rounds of the Irish and Ulster Short Circuit Championships.
The race was scheduled to take place in early August last year but was shelved because of a lack of sufficient entries.