Hudson Young's proposed deal would have kept him in Canberra until 2032, when the NSW backrower would be 34.
Canberra officials had offered him a four-year contract worth $4.4 million, the richest deal in the club's history.
Deep into negotiations, they raised the possibility of adding a fifth season to secure his signature.
Young and his management remained noncommittal, however, and Canberra felt discussions had gone on too long.