With his 300th match a loss to Adelaide at AAMI Stadium in round 12, Simpson faced a date with Port Adelaide at the same venue to conclude his career, unless he chose to play on in 2010.
Because his 250th match was also played interstate – against Carlton on the Gold Coast in 2007 – Simpson admitted there was some selfishness in keeping his swansong in Melbourne.
That was why he chose Friday night's clash with the Blues, even though North has one more home game against the Demons a week later and meets St Kilda at Docklands in round 21.
"We'd already started a bit of an action plan based around that (Simpson's farewell) anyway," Crocker said.
"He just called it three weeks earlier."
Crocker sat down with Simpson last Monday night, but had sensed the veteran's retirement was imminent.
Simpson had been obviously frustrated in round 16 against Richmond – a match that finished in a draw after North had trailed by 42 points at half time.
"He approached me after the Richmond game down at the beach when they were doing their recovery and said he wanted to catch up," Crocker said.
"I knew this was probably what he wanted to catch up about.
"He's a deep thinker about the game, where he's at, what role he plays in the team and the direction of the club. He obviously felt it was a really good time for him to walk away and give some other guys an opportunity to fill a very big pair of shoes."
Collecting 34 possessions, Simpson was the Roos' best player in Saturday night's loss to the Brisbane Lions, and broke the news to his teammates during the post-match recovery session in the hotel pool.
He told the remainder of the squad and staff on Monday morning.
Crocker agreed that, unlike some past players at other clubs, Simpson had remained in North's better performers this season and was not holding onto a position that a developing teammate deserved more.
"He's been able to play his part this year," Crocker said.
"His preparation has always been very good and his durability's good, which has allowed him to keep his performances at a high level."
Though he was unable to confirm the role the former captain would have for the last four weeks of the season, Crocker confirmed he would have Simpson's coaching aspirations in mind.
"He's very keen to pursue a coaching career, and whatever the club can help him with in relation to that, I'm willing to sit down and work out what he needs to do over the next month," Crocker said.
"There's no doubt he could walk straight in to an AFL assistant's role, but it's up to him which pathway he wants to take. I know he's toying with (Michael) Voss and Nathan Buckley and those guys who have gone through the AIS-AFL Academy program.
"He'll really be able to weigh up whatever opportunities come, and I'm sure there will be plenty."
