Marcus Rashford endured another frustrating afternoon for Manchester United on Sunday and has been told how to become a more complete striker by legendary No.9 Alan Shearer.In his most recent outing for the Red Devils, the England international drew a blank before being forced off through injury.United suffered a 2-0 defeat away at West Ham, with Ole Gunnar Solskjaer’s side seeing their standards dip as a collective once again. Article continues below Editors’ Picks Ox-rated! Dream night in Genk for Liverpool ace after injury nightmare Messi a man for all Champions League seasons – but will this really be Barcelona’s? Are Chelsea this season’s Ajax? Super-subs Batshuayi & Pulisic show Blues can dare to dream Time for another transfer? Giroud’s Chelsea spell set to end like his Arsenal career They have been looking for Rashford to provide inspiration in the final third, but have seen him deliver only three goals this season – with two of those being penalties.He could now be facing up to a spell on the sidelines and, with Anthony Martial also nursing a knock, 17-year-old Mason Greenwood may be forced to step up into a regular role.United will be hoping that Rashford is not out for long, but Shearer admits that there are areas of his game that need to be improved whenever he finds himself back on the field.The former England frontman, who remains the all-time leading goalscorer in Premier League history, knows all about what it takes to be a prolific presence and feels the Red Devils – managed by ex-striker Ole Gunnar Solskjaer – need to work on providing more of a threat.Shearer told Match of the Day: “The problem that Man Utd have got is that 19 games, scored 17 in all competitions, four of them were against Chelsea, and this is the reason why – because no urgency, no spark, no creativity.“Mata should go forward [when he had the ball inside West Ham half], he should go forward, but instead he chooses to go backwards.“It’s a nightmare for forwards, they were slow, had too many touches.“If Rashford wants to play centre-forward and he wants to score more goals, which I’m sure he does, he has to do better than this.“His movement has to be better, he has to move for the ball and attack the ball instead of waiting for the ball.“I’d be concerned if I was him (Solskjaer), because they’re not creating enough chances.”Solskjaer has been warned by former United midfielder Roy Keane that he may not get the time he needs to turn the Red Devils around unless he starts addressing issues such as those which exist up front in his side.United will be back in action on Wednesday when they face Rochdale in the third round of the Carabao Cup, before then taking in another testing Premier League encounter with Arsenal. Check out Goal’s Premier League 2019-20 fantasy football podcast for game tips, debate and rivalries.