Roy Keane has urged Manchester United fans to give Louis van Gaal up to three years to prove himself at the Old Trafford helm . The Dutch manager oversaw another disappointing performance and result in United 's 2-1 FA Cup defeat by Arsenal at Old Trafford on Monday night . Danny Welbeck returned to his old stomping ground to score the winner after Wayne Rooney levelled Nacho Monreal 's strike in the first half , but it was yet another lacklustre display under Van Gaal that irked United supporters . United 's legendary midfielder Roy Keane says Louis van Gaal should get more time in charge at Old Trafford . Van Gaal came under more criticism for another lacklustre display in the 2-1 FA Cup defeat by Arsenal . Keane was in the studio with former England stars Gary Lineker , Alan Shearer and Ian Wright . Their hero Keane , however , maintained the manager needs more time with fans unaware of what the job entails . 'Van Gaal is going to get criticised , you 'd expect that , ' Keane said during his BBC Match of the Day analysis . 'Give the man a chance - two or three years . A lot of fans do n't quite understand how to run a football club as big as Manchester United . 'They should have given David Moyes more time but did n't . What are they going to do ? Chop and change again ? Van Gaal has been in the door two minutes . It takes time . It 's literally a rebuilding job . A dismayed Marouane Fellaini ( left ) , Michael Carrick ( centre ) and Wayne Rooney after Arsenal 's winner . Danny Welbeck broke the hearts of his boyhood club by pouncing on an error to send Arsenal to Wembley . 'It would be a disaster if United do n't finish in top four . The big problem with people at the club and ex-players is they keep looking back comparing teams from 10 years ago . 'They have got to look forward . Focus on the players , focus on the manager ... get right behind him . I still think they have enough to get in that top four . ' Keane 's old sparring partner , former Newcastle and England striker Alan Shearer , was more damning . He said : 'Manchester United 's main priority this season is finishing in the top four . If they do n't then it will be a catastrophe . 'They have spent a lot of money on players . There 's a hell of a lot more money that needs to be spent to get them anywhere near where they want to be . 'There is n't another team in the Premier League that passes it back more than Manchester United . ' Wayne Rooney 's flying header to equalise for United in the first half could n't stop his side crashing out . Angel Di Maria 's red card was the final blow for United as Van Gaal 's troops lost their heads . Keane and Shearer 's battle of words during the BBC 's FA Cup analysis were nothing compared to what the hot-headed duo got up to in their playing days . Neither was a player the opposition wanted to get on the wrong side of , so no battle was more fierce than when the two clashed . Keane lashes out at Shearer when the two came to blows at St James 's Park in 2001 . The former United captain named Shearer as a player he 'always had in the back of his mind ' in his recent autobiography The Second Half alongside other famous foes like Patrick Vieira and Alf-Inge Haaland . Keane made it clear that although he regularly came across Alan Shearer while working as a TV pundit , there is little or no chance of them ever building bridges such is the mutual dislike of each other . Keane picked Shearer out as a player he always had in the back of his mind alongside Patrick Vieira . The most famous flashpoint came in 2001 at St James ' Park . The two skippers came head to head and Keane was shown a red card for lashing out at the England man . It was the first time the former United maestro had appeared in the BBC studio after a long association with terrestrial rivals ITV . Keane has to be held back by David Beckham during the infamous row that saw the United man sent off .
Keane : 'Fans do n't quite understand how to run a club as big as United ' Van Gaal oversaw another poor performance in the four-1 defeat by Arsenal . Danny Welbeck came back to haunt United by netting the winner . United now have no chance of silverware after crashing out of the FA Cup . READ : Van Gaal walks out of Man Utd press conference on a sour note . CLICK HERE for all the latest Manchester United news .