<text>  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 Uniteds 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 Monreals strike in the first half, but it was yet another lacklustre display under Van Gaal that irked United supporters. Uniteds 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, youd 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 dont quite understand how to run a football club as big as Manchester United. They should have given David Moyes more time but didnt. What are they going to do? Chop and change again? Van Gaal has been in the door two minutes. It takes time. Its literally a rebuilding job. A dismayed Marouane Fellaini left, Michael Carrick centre and Wayne Rooney after Arsenals 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 dont 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. Keanes old sparring partner, former Newcastle and England striker Alan Shearer, was more damning. He said: Manchester Uniteds main priority this season is finishing in the top four. If they dont then it will be a catastrophe. They have spent a lot of money on players. Theres a hell of a lot more money that needs to be spent to get them anywhere near where they want to be. There isnt another team in the Premier League that passes it back more than Manchester United. Wayne Rooneys flying header to equalise for United in the first half couldnt stop his side crashing out . Angel Di Marias red card was the final blow for United as Van Gaals troops lost their heads . Keane and Shearers battle of words during the BBCs 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 Jamess 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 . 