Sir Alex Ferguson has expressed his frustration about the way football agents have "an imagination beyond belief", as he revealed some of the extraordinary demands he had encountered at Manchester United, including one transfer when the club were asked to buy a block of apartments as a condition of the player joining the club.

The agent, according to Ferguson, had asked for "a box of flats" for the deal to happen. He told another story of one middleman who wanted his client, a prolific striker, to be paid for each goal he scored. Ferguson did not name the people involved but made it clear he had informed the club's directors to refuse. "I said: 'Can you please remind him that's why we are buying [the player] in the first place – because he is a goalscorer?' This is what you're dealing with; it's unbelievable."

Ferguson was reflecting on the perceived role of Wayne Rooney's adviser, Paul Stretford, when the striker handed in a transfer request in October. United's suspicion has always been that Rooney, despite his denials, had been tempted by the idea of joining Manchester City, where Stretford is an associate of the football administrator, Brian Marwood, who previously worked as an executive at Nike, the player's sponsors.

Ferguson said: "I think he [Rooney] took bad advice and when he saw the impact of the fans and my response he realised – and I'm sure plenty of people told him – that he was making a big mistake."

Stretford once had a strong working relationship with Ferguson, helping to put in place Rooney's transfer from Everton in 2004 as well as being Andy Cole's representative when he signed from Newcastle United in 1995, but the Scot now regards the former vacuum cleaner salesman as "not the most popular man in the world – certainly at our club".

He has also been angered recently by the influence of the London-based agent Jerome Anderson at Blackburn Rovers, where Sam Allardyce, one of Ferguson's close allies, was sacked last month. "Jerome Anderson couldn't pick his nose," Ferguson said in the days after Allardyce's dismissal.

His latest comments were made in an interview on RTE Radio 1 in which Ferguson reflects on the Rooney dispute by emphasising that "the most important person at Manchester United is the manager", adding that "the minute a player becomes more important than the manager our club is finished, we'll never be the same again".

Addressing the role that agents play in players' wages, Ferguson said: "When I get annoyed is when managers phone me and say such-and-such player – and I'm talking about players who couldn't lace my reserve‑team players' boots – is asking for £1m a year. That's when it becomes disappointing ... the way some agents work a miracle by getting these terms for players who are not stars.

"At United I think most of my first-team players deserve what they're getting. They're playing in front of 75,000 people every week, they're achieving, successful, good footballers, honest professionals. They produce on the field, they bring people into the grounds, and they deserve it. But there are some players at other clubs who get paid enormous amounts of money and I don't know why."

The irony is that one of Ferguson's sons, Jason, once worked as an agent and was the subject of a Panorama documentary in 2004. Ferguson now says he has no contact with agents. "I don't deal with them directly but [the chief executive] David Gill has to, and it's hard job. They have an imagination that is beyond belief."