Former Scotland coach Kenny Black says Craig Levein was frustrated by results but had hoped to be given more time as manager of the national team.
Straightforward
Black revealed there was no prospect of him staying on when he spoke to Regan on Monday.
"It was straightforward to me - once Craig leaves the post I go with him," he said.
"They did sound me about my thoughts about going on the trip and I explained to Stewart the Luxembourg one would be very, very difficult for me to go on because I was part of a team along with Craig and Peter (Houston) and once the decision was made about Craig it was straightforward for me to walk away."
Despite Levein's belief he deserved more time, the SFA board ultimately agreed with many fans that three wins from 12 competitive games was not good enough, and Black found the record difficult to explain.
"I can't quite put my finger on that one," he said. "We had some really, really good friendly results. Obviously that doesn't make it any easier to qualify.
"We were in a really tough group for the Euros against the world champions and the Czech Republic were the team we were gunning for.
"The game against Spain was a lot more like ourselves when we battled back to 2-2 and we were unfortunate not to take something from the game.
Legacy
"There were definitely some positives in the friendly results but the negative was the qualification results weren't as good as we would have liked.
"One or two decisions didn't go our way, the Czech Republic game at home and the decision to disallow Steven Fletcher's goal down at Wales."
But Black believes Levein has left a good legacy to his successor.
"There is no question the squad is a lot stronger," he said. "You just need to look at the guys in the squad who are plying their trade down in England in the top division.
"There has been a lot of work behind the scenes to promote the younger ones coming through.
"Unfortunately Craig will not be there to see the fruition but over the next few years I'm sure things will take an upwards curve for Scotland."
