Sir Alex Ferguson admits his tough approach to discipline could have cost him Premier League titles during his time at Manchester United.
Ferguson, who won 13 league titles at United, had a number of high-profile bust-ups with some of the best players in the world during his 27-year tenure at Old Trafford.
David Beckham, Roy Keane, Jaap Stam and Ruud Van Nistelrooy - among others - incurred the Scot's wrath during his trophy-laden spell at the club.
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Ferguson says he has no regrets about taking a hardline approach with his players, but admits the policy may have cost him silverware.
"People will give a manager plenty of opportunities to crack the whip so it's best to pick and choose your moments," the former United manager writes in his new book Leading, which is out on September 22.
"You don't have to dish out a punishment very often before everyone gets the message.
"I place discipline above all else and it might have cost us several titles.
"But if I had to repeat things I'd do it precisely the same because discipline has to come before anything else."