Crocker, 42, played in North's 1996 premiership before succumbing to a knee injury and retiring in 1998.
He moved immediately into coaching, overseeing VFL side Port Melbourne in 1999.
In 2000 he moved to Richmond, where he served as an assistant coach until being lured back to Arden St in 2004 as an assistant coach in charge of defence.
He has since become regarded as the Roos' senior assistant, and was favourite to step in as caretaker coach.
Laidley informed the club of his decision to quit on Tuesday morning, bringing to an end his seven years at the helm.
North are currently undergoing a review of coaching, which was slated to conclude before round 16. But Laidley's decision buys the club more time.
