Juan Mata's goal at Town should not have stood

The Spaniard scored United's second goal in the 3-0 win at Greenhous Meadow on Monday night.

But three United players were stood behind the wall, obscuring the view of Town keeper Jayson Leutwiler.

They were then were in an offside position when Mata struck the ball and, in fact, were still in an offside position when the ball went over the defensive wall.

Officials allowed the goal to stand before Jesse Lingard added a third after the break to clinch United's spot in the quarter-finals at home to West Ham.

United manager Louis van Gaal claimed they got the idea from their Europa League opponents Midtjylland and added they were told they were allowed to have men positioned behind the wall.

But the Premier League said: "In situations where an attacking player adopts an offside position for a clear tactical purpose, and then remains in an offside position when the ball is last touched/played by a team-mate, they "run the risk" of being penalised for interfering with an opponent, if they: a) clearly obstruct the line of vision of an opponent or b) make an obvious action that clearly impacts the ability of an opponent to play the ball.

"Proximity and position of the attacking player(s) in an offside position relative to the opponent (usually the goalkeeper)

"Obvious action (including movement) of the attacking player(s) in an offside position

"The three United players (Jesse Lingard (number 35), Ander Herrera (21) and Anthony Martial (9)) position themselves between the ball and the goalkeeper (Figure 1).

"Herrera also looks directly at the keeper when establishing the position of three attacking players. This emphasises tactical purpose.

"As the free-kick is taken, the three all make a clear movement (or "obvious action"), which clearly impacts on the ability of an opponent to play the ball (see Figure 2).

"In this, and similar situations, the attacking player(s) in an offside position would be expected to be penalised for interfering with an opponent."