Former Manchester United manager Alex Ferguson has urged everyone connected to the club to have "some patience" as current boss Louis van Gaal tries to bring the glory days back to Old Trafford. United has yet to win any silverware since Ferguson retired in 2013 after guiding the English giant to 28 trophies in 26-and-a-half-years in charge. Immediate successor David Moyes was sacked after less than a season in charge in May 2014 and this term has seen Dutch manager van Gaal come under intense pressure after United went out of the Champions League at the group stage and was knocked out of the Europa League by archrival Liverpool, having already been beaten in the League Cup by second-tier Middlesbrough. United, however, is now just a point off the top four and has a FA Cup semifinal replay to look forward to, but that hasn't stopped the chorus of criticism over what many fans see as a lack of attacking football. However, Ferguson, in an interview with Sky Sports Thursday, said: "It is dead easy to be critical. "You have to be realistic about some things — the number of injuries he (van Gaal) has had: Phil Jones has played only seven games this season, Ashley Young, (Antonio) Valencia, (Luke) Shaw, these are big losses." Ferguson, whose career total of 49 trophies (he won 11 while in charge of Scottish club Aberdeen) makes him British football's most successful manager, added: "It doesn't matter which team you are, if you have players missing of that caliber it has to have an impact on the team. "The other aspect which is always easy to forget there are also five new players in their first season at United, and two are young players in (Anthony) Martial and Memphis (Depay) and their promise is good," the 74-year-old Scot explained. "You have to have some patience being a Manchester United fan and they have shown that over the years; in Matt Busby's time, in my time," said Ferguson in a reference to celebrated Scottish predecessor Matt Busby, who brought success to Old Trafford in the 1950s and 1960s. "For 150 years of history it is worth having a couple of years on the quiet side of success because they will always come back and come back strong." United's injury crisis has seen van Gaal turn to the youth set-up for first-team players, the manager maintaining a tradition that started with the ‘Busby Babes'. Teenage striker Marcus Rashford, a locally-born 18-year-old, has led the way with five goals in eight appearances. "You have to give him credit, he's given nine young players their debut. I think the future is good," Ferguson said of Van Gaal. "Rashford is an example of what I think is Manchester United. They are the one club in England who will always identify a Rashford and give a young kid a chance — there is no better club in England at giving young kids a chance. "Rashford is a sensation and one of the best in years." Meanwhile, Ferguson had a warning for incoming Manchester City manager Pep Guardiola, who will bid to return United's "noisy neighbors" after guiding current club Bayern Munich and former side Barcelona to domestic and European success. "Man City have made a real coup in getting him but Pep won't find it easy, English football is not easy," he said of the Spaniard's imminent arrival in the Premier League. "Every foreign coach that has come to England will tell you that. "Pep will be a success but I don't think he'll ever replicate what he did at Barcelona because that was a high standard — they were the best. "Pep will improve City but Arsenal, Liverpool, Chelsea, Tottenham will want to do something and will be desperate to win the league next season as much as City, so for Pep there is not a guarantee they can win the league."