Sir Alex Ferguson is widely regarded by football fans as the greatest football manager of all time and deservedly so.The retired Scottish coach won three Scottish Premier Division titles with Aberdeen - plus four Scottish Cups and the European Cup Winners’ Cup - before moving to Old Trafford in November 1986.Ferguson exceeded all expectations at Manchester United, winning an unprecedented 13 Premier League titles, five FA Cups, four League Cups and two Champions Leagues.He built several hugely-successful teams during his 26-year tenure at the Theatre of Dreams before calling time on his glittering managerial career in the summer of 2013.The post-Ferguson era has been difficult for Man Utd, to put it mildly.They’ve failed to win another Premier League title over the past seven years and have been through four different managers.Rio Ferdinand was one of Ferguson’s best ever signings and the retired defender, speaking on BT Sport on Friday, recalled a fascinating story about his former boss.p1ef7cqh441d4usql1bta192vajeb.jpgAsked by Gary Lineker if he’d ever been left baffled by any of Ferguson’s decisions, Ferdinand explained how the Man Utd legend proved him spectacularly wrong just minutes after kick-off in a massive European tie.United played Bayern Munich in the 2009-10 Champions League quarter-finals and needed to beat their German opponents at Old Trafford to stand any chance of reaching the last four.Ferguson sprang a big surprise with his starting line-up, naming Darron Gibson in a midfield three alongside Darren Fletcher and Michael Carrick.p1ef7cu9frsge1bl1111ova81soed.jpgRyan Giggs and Paul Scholes were both named among the substitutes.“Darron Gibson came in once and he wasn’t a regular starter. No disrespect to Darron Gibson, we were sitting there, Bayern Munich at home, we need to get out there and score a goal.“‘Why’s he playing him?!p1ef7cv2ve13e91ddc9cv5fv1603f.jpg“Within two minutes, Darron Gibson goes and scores the first goal.“You look at the bench and think ‘this geezer’s a genius’.”p1ef7d0bpki6elb68hm1oiq543h.jpgWatch Ferdinand tell his story in full here…

United managed to win the match, thanks to two further goals from Nani, but they were knocked out of the tournament on away goals when Arjen Robben scored a quite brilliant left-footed volley in the 74th minute.

Gibson, meanwhile, lasted another two years at Old Trafford before moving to Everton.

The former Republic of Ireland international joined Salford City earlier this year.

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He may not have been a top-level footballer in the same way Giggs or Scholes were, but Ferguson still knew better than anybody which of his players to select and when.

Most of his gambles paid off - and Rio knew never to doubt his manager again.