Former Manchester United boss Sir Alex Ferguson made private calls and exchanged text messages with Premier League referee Mark Halsey during his time at the Old Trafford helm, it has been revealed.
Halsey - who retired from refereeing at the end of last season - made the startling revelations in his book Added Time.
As reported by the Daily Star, ex-United chief Ferguson was contacted by Halsey last year and was asked to defend fellow whistleblower Mark Clattenburg, who was caught up in the centre of a race row involving Chelsea midfielder John Obi Mikel.
Clattenberg was later cleared by the FA of any wrong-doing, but Halsey's admission that he shared text messages with Ferguson has caused yet more controversy.
Halsey wrote: "I took matters in my own hands and rang Sir Alex asking him to speak out.
"He agreed and used his Friday press conference to say he could not conceive of Mark saying such things. It helped the situation a great deal."
Halsey went on to write about his relationship with the former Manchester United boss in greater detail, but insisted that everything was kept above board and professional.
"It took time to gain Sir Alex Ferguson's respect but in the end we had a very good relationship," Halsey added.
"One thing should be made clear about my relationship with Sir Alex.
"I may have spoken to him a lot and shared texts but he knew when I crossed that white line there were no favours.
"Players and managers would not respect you if you gave decisions based on friendship."
Manchester United will be hoping to put any talk of refereeing controversies behind them as they return to action tomorrow, with David Moyes' men playing host to Bayer Leverkusen in the Champions League.