On a day of big-name returnees with James Tedesco, Dylan Edwards and Bradman Best all chances to come back from injury, Horsburgh was the most notable absentee from team lists.
The Raiders prop is signed with Canberra until the end of next season, but has been linked with a move to the Broncos for 2027.
That came before Horsburgh drew the ire of Raiders coach Ricky Stuart on Sunday, when he was sin-binned for slapping Dane Gagai late in the 30-24 loss to the Knights.
"It was a f***ing brain explosion, and we lost the opportunity," Stuart said afterwards.
"We lost the start of the season because we were self-entitled and undisciplined and (now) we've lost the opportunity to continue trying to make the semis."
Stuart responded on Tuesday by leaving Horsburgh out of his side to face Cronulla, with Ata Mariota instead moving to prop.
Elsewhere, Manly's faint finals hopes have taken a further hit with Tom Trbojevic's return from a hamstring injury held off for another week.
The Sea Eagles have instead turned to Clayton Faulalo to come back from his own hamstring tear at No.1 for the must-win clash with the Dolphins.
Ben Trbojevic is also still out after suffering a second concussion in two weeks last month, while Manly have Nathan Brown and Simi Laiafi starting while four first-choice props are out.
Manly players remain adamant their season is not over after dropping from third to 10th with five straight losses, with Faulalo impressing at the back while deputing for Tom Trbojevic earlier this year.
Cronulla have also lost Jesse Ramien to a pectoral injury, with the Sharks still unsure how long their strike centre will spend on the sidelines.
There is better news for the Sydney Roosters with Tedesco named to return from an ankle injury against Penrith, who have Edwards (shoulder) listed on an extended bench.
Bradman Best and Phoenix Crossland have been named to return for Newcastle against Gold Coast after overcoming calf injuries.
And Campbell Graham (calf) is back for South Sydney in their crunch clash against Canterbury, with Jayden Sullivan named at No.7 to replace the injured Ashton Ward.
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