The whole is still weaker than the sum of its parts at United despite victory over Preston...

Manchester United laboured to a 3-1 win over Preston as problems remain for Louis van Gaal, writes Matthew Stanger...

Manchester United eventually squeezed past the League One outfit to set up an FA Cup quarter-final against Arsenal, but this was another night on which they struggled to assert themselves against lower-league opposition. 

It is becoming a not entirely unwelcome habit for Van Gaal's side to play poorly but grind out important results, although the manager has long outlived his three-month forecast to impress his ideas upon the team. It was not until Marouane Fellaini again moved into attack that United broke down their League One opponents, with that favoured tactical switch not of the style supporters are accustomed to.

Van Gaal is on course to achieve his main objective of guiding the club back into the Champions League at the first attempt but, as with the 1-0 defeat to Southampton at Old Trafford in January, there is a lingering feeling that another slip up is just around the corner. At present, the whole is weaker than the sum of its parts, with Van Gaal struggling to marry results with convincing performances.

The manager's selections have been debated with relish during a stuttering run of form, but on Monday Wayne Rooney returned to the attack with Angel Di Maria picking up a familiar position on the left. And still United failed to find their rhythm.

Ander Herrera, starting only his fourth match since October, was one of the main culprits in the first half. Perhaps feeling under pressure to impress after Van Gaal's revelation about wanting a new midfielder in the summer, the Spaniard struggled to impose himself before the interval and was guilty of setting up a quick Preston counter-attack after playing the ball blind and conceding possession.

Herrera's contribution improved in the second half - in which he eventually scored the equaliser - but the same could not be said for Radamel Falcao, who remained anonymous throughout his 60 minutes. After failing to manage a single shot or create a chance for one of his teammates - and recording just 24 touches of the ball - the Colombian was replaced by Ashley Young as Van Gaal went back to basics to maintain his last hope of silverware.

The change worked, just as it did in the recent 1-1 draw at West Ham, yet it seems United are no closer to fashioning a formula for winning with conviction. That they didn't record an attempt on target in the first half - while Preston had two - and only one before Fellaini's switch, highlights the Belgian's necessity in a more direct approach. But should a team with Di Maria's talent in midfield feel the need to bypass such obvious quality?

It is not only in attack that United are lacking confidence, either. They have made 20 errors leading to shots in the Premier League - four more than any other side - and were caught backpedalling on a number of occasions as Preston pushed for a second goal. Marcos Rojo's late tumble under pressure from Callum Robinson summed up the contagious hesitation, while Scott Laird was allowed time and space in the box to fire the hosts in front.

"We showed a team spirit, unbelievable," said Van Gaal afterwards. "Then we changed the shape and that was the solution." 

It may have been the short-term fix to secure safe passage to the quarter-finals, but the problems with United's style of play are now extending into the long term.