BRYAN ROBSON has told Manchester United chiefs to back Ruben Amorim for the long haul and slammed the club’s recent history of signing flops.The United legend says the revolving door of managers since Sir Alex Ferguson’s retirement in 2013 has wrecked any chance of stability, and insists under-fire former Sporting Lisbon boss must be given at least THREE years to fix the mess.GettyRobson moved to United for a British record transfer fee of £1.5 million in 1981[/caption]AFPRobson has backed Amorim to get things right at United[/caption]Shutterstock EditorialManchester United stars are under-performing despite Amorim being in charge for the last eight months[/caption]Speaking to The Telegraph, Robson said: “We’ve changed managers that many times since 2013.“I feel you have to stick and say, ‘No, we are not sacking the manager. We are not blaming.’“When you have a little bit of money and the club are going to allow you to change your squad, you need three years to get the team right.“For me, three years at Manchester United should be enough.”Amorim, 40, has had a disastrous start to life as United boss, winning just eight of his first 31 games. But Robson is urging the board to give him more time, despite fans on social media calling for his sacking.Robson didn’t hold back when reflecting on the transfer blunders of the Ed Woodward era, suggesting too many signings simply weren’t up to scratch.He fumed: “Look at the money we spend. It’s up to you to go around the world and get top players who are going to improve you.”BEST ONLINE CASINOS – TOP SITES IN THE UK“I think five years ago some of the players we bought were just not good enough to be Manchester United players. It’s an accumulation of that.”And Robbo, who captained United through some of their most hard-fought years, believes the club lost its way by ignoring experienced Premier League stars in favour of flashy foreign names. “The other thing I think we went away from is getting good, experienced Premier League players.“So when they get to 28, you bring them on board if you can. There have been loads of players who have left clubs.”And his message to United’s decision-makers couldn’t be clearer.He added: “When I was in management, I believed that if you bought average players, you got an average team.”United will get a chance to bounce back from their derby defeat to Manchester City last weekend when they host Chelsea in Saturday’s late Premier League kick-off at Old Trafford.AFPRobson also called out the signnings under Ed Woodward[/caption]