Aaron Mauger's impending move to Leicester has been considered acceptable because the Tigers don't play in the same competition as the Crusaders, but Matson's meeting with opposition players with a view to joining their team is a clear conflict of interest and doubly so in the shadow of another clash between the two franchises on June 6.
The whole issue is a huge distraction for the Crusaders as they seek to maintain their record of making the playoffs every year since 2001.
The Crusaders will likely ask defence coach Matson to resign his New Zealand Rugby contract if he indicates he is ready to leave them for the Blues, despite the potential fallout it would cause during a pivotal time in their season. Some of their players are understood to be talking about the issue, however, and there is a feeling that there is an important principle at stake.
The Matson decision could come to a head this week.
A precedent was set recently just down the corridor at the Crusaders' Rugby Park headquarters. When Canterbury assistant coach Jason Holland confirmed he would take over as Hurricanes assistant alongside Chris Boyd from next year it is understood he was told to vacate his desk that afternoon.
Kirwan conceded defeat on his team's chances of making the finals over a fortnight ago after they lost to the Crusaders in Christchurch and he has been able to ramp up his efforts towards saving his job.
However, it is understood he has been talking to Matson - a key figure in his application to the Blues board recently - since March.
The board is apparently happy with Kirwan's proposal, and his willingness to change for the better, to the extent that Kirwan's job will not be re-advertised despite three seasons of under-achievement.
New Zealand Rugby - ostensibly the employers of Kirwan and Matson as the pair are on NZR contracts - also appear willing to go along with the plan which apparently includes the promise of the head coaching job to Matson in 2017.
The Crusaders are understood to have made a big offer to keep Matson, but the former All Blacks and Crusaders midfielder appears set on furthering his coaching ambitions in Auckland.