Two decades on, the Hoops utility man remains grateful for the timely intervention that has let him flourish with his boyhood heroes.
This weekend, Celtic will mark the 20th anniversary of McCann's last-gasp Parkhead takeover.
In 1994, the ailing Glasgow giants had just 7000 season-ticket holders, played in a crumbling stadium and were being driven into the ground by a dysfunctional board.
When McCann left in 1999, Celtic Park was a shimmering 60,000-seat arena with over 40,000 season-ticket holders and the Scots-Canadian businessman had helped put in place a financial plan to safeguard the East End club for years to come.
Scotland cap Mulgrew is one of the current generation reaping the benefits of the McCann legacy and expressed his gratitude as he reflected on the most turbulent, but ultimately triumphant, chapter in Celtic's history.
He said: "I was young when Fergus arrived but I've heard a lot since. I vaguely remembered when the club were struggling and I know how good he was for Celtic.
"As a supporter and player, I'm really thankful for what he did. The players who know about Fergus are appreciative of what he did. He turned the club around and played a big part in the Celtic we know now.
"A lot of fans didn't fully understand what he was doing for Celtic. But what a clever person he was. He transformed the place and we're all very thankful for it now.
"It's hard to believe he was booed once as he unfurled a flag. You can't imagine that happening now. But the supporters didn't realise back then how great he would be for the club. He was accused of being a bit tight.
"But now? As a fan, I can't thank him enough.
"Every time we run out at Celtic Park, a fantastic big stadium, you realise it was Fergus who gave us it. He did huge things for Celtic and I'm sure anyone who doubted him realises they were wrong."
McCann's policy of prudence came when city rivals Rangers upped the arms race with the big spending that would eventually lead to financial catastrophe.
Mulgrew added: "He was ahead of his time and he knew what he was doing. There are a couple of clubs now who could do with a Fergus McCann.
"People didn't have a clue what he was trying to achieve back then. Some people thought he was robbing the club and I think that's why he was booed.
"Celtic were very close to folding before Fergus came in but look at the club now. That shows how clever he really was."