But when Michael Owen scored the winner in the sixth minute of injury time in a 4-3 home victory over neighbor Manchester City on Sunday, Ferguson had his answer ready.
No matter that he had sold the Portuguese star who contributed 66 goals to United's three Premier League titles. He had even sold Ronaldo to Real Madrid, one of the club's biggest rivals in the Champions League.
Who cares that he let Argentina striker Tevez go to the ambitious and super-wealthy team from the other side of Manchester? Tevez dispossessed goalkeeper Ben Foster to set up City's first goal but Fergie needn't have worried.
At the end of the game, the 67-year-old Scot was dancing a jig of delight after a victory which was typical of United and pure Ferguson.
Although his team lost the lead three times in a thriller, a striker he signed for nothing struck the winner against a City side on which $194 million had been lavished during the offseason.
While Ferguson hugged his players, Owen's goal had City manager Mark Hughes fuming at the amount of time the referee had added on.
It was as if the winner was destined to come from Owen, someone who had lost his way after injuries and transfers, was repeatedly ignored by England coach Fabio Capello and was considered a major gamble by Ferguson.
The fact that he scored such a dramatic late winner against City justified that gamble as far as the United fans were concerned. The goal represented yet another victory for the United manager who has led the club to 11 Premier League titles in 17 years and 25 trophies in his 23 years at Old Trafford.
Ferguson has made plenty of mistakes, such as expensive signings who failed to deliver and selling stars who did little at Old Trafford but did well elsewhere. He famously fell out with the likes of David Beckham, Roy Keane, Ruud van Nistelrooy, Gordon Strachan and Jaap Stam who all left the club sooner than they expected.
But he has a knack of getting under the skin of his rivals and Hughes, who played under Ferguson from 1988-95, follows a long line of managers who have been outthought by the cunning Scot.
At the start of the season, when City was stockpiling stars and spending the huge wealth of its Abu Dhabi owner, Ferguson took some of the pressure off his own team by saying his neighbor was getting most of the attention.
He effectively put more pressure on City by building the level of expectation at a club which has not won the league title since 1968.
Before Sunday's game, Ferguson accused City of being cocky and arrogant in flaunting its capture of Tevez and, after the victory, he was crowing that his side had beaten its "noisy neighbor".
"There has been a lot of expectation on Manchester City and with the spending they have done they have to win something," Ferguson said. "Sometimes you have a noisy neighbor and have to live with it.
"You can't do anything about them if they keep on making noise but what we can do, as we showed today, is you can get on with your life, put your television on and turn it up a bit louder."
As far as Man City is concerned, United has been its noisy neighbor for around 40 years and, with Ferguson in charge, shows no sign of turning down the volume.
"As far as the players are concerned, they showed their playing power," Ferguson said. "And that's the best answer of all."