Manchester United legend Roy Keane has claimed that Brian Clough was a better manager than Sir Alex Ferguson.

Keane played under both coaches at Nottingham Forest and United respectively, and the former Republic of Ireland captain admitted that pair were the two greatest managers that he worked with.

However, speaking in his new autobiography, Keane said that Clough's more personable approach had a greater impact on him during his career.

Keane said: "I worked under two great managers and I put Brian Clough ahead of Alex Ferguson for a simple reason. What was the most important thing in my football career? Brian Clough signing me. That kick started everything.

"[They are] different managers, both brilliant. I think Clough's warmth was genuine. I think with Sir Alex Ferguson it was pure business – everything is business. If he was being nice I would think: 'This is business, this'.

"He was driven and ruthless. That lack of warmth was his strength. United was a much bigger club than Forest but his coldness made him successful."

Keane's book, titled The Second Half, is released later this week.