Ferguson retired after 26 years at Manchester United over the summer, handing over the reigns to David Moyes.
And the ex-Toffees boss has struggled at Old Trafford so far, losing 2-1 at home to West Brom at the weekend.
And Macari, who spent eleven years at United in the 1970s and 1980s, believes the Scot may have realised the weaknesses in the first-team before calling it a day at the end of last season.
“He’s always been a good judge of everything,” he told talkSPORT.
“When he shocked everyone and said he was retiring, I thought, ‘is he aware of what’s around the corner, is he taking the view that one or two of his best players are coming to an end’?”
And Macari went on to say that Moyes should have strengthened further in the summer transfer window.
"“Every team in the country needs new blood,” he said. “The supporters get tired of watching the same players.
“I just felt this summer he needed to bring in some new players. They brought in one main player [Marouane Fellaini] but he wasn’t the sort of player the supporters wanted to see. They wanted a little ball playing midfielder.”
That midfielder could have been Cesc Fabregas or Athletic Bilbao's Ander Herrera - two players United were linked with in August.
In the end, they missed out on their top targets and signed Fellaini on transfer deadline day.
The Belgian international is still being eased into the squad, but United's results have been shaky so far this term.
They have an excellent chance to dampen the criticism tonight though, when they take on Shakhtar Donetsk in Ukraine in the Champions League.