The Scottish manager, who retired at the end of last season, signed the Australian goalkeeper in the summer of 1999 to replace Peter Schmeichel.
However, writing in his new autobiography, Ferguson has revealed that the 41-year-old's eating habits meant that he was never going to be a success at Old Trafford.
"Mark Bosnich was a terrible professional," wrote Ferguson. "We played down at Wimbledon and Bosnich was tucking into everything: sandwiches, soups, steaks. He was going through the menu.
"I told him, 'For Christ's sake, Mark, we've got the weight off you, why are you tucking into all that stuff?'
"We arrived back in Manchester, and Mark was on mobile phone to a Chinese restaurant to order a takeaway. 'Is there no end to you?' I just couldn't make an impact on him."
Bosnich departed United in 2001 for Chelsea.