The Spaniard’s 45th minute free-kick put his side 2-0 up and all but booked Louis Van Gaal’s men a place in the quarter final against West Ham.
But the goal and, more specifically, the deployment of a three-man wall comprised of Anthony Martial, Jesse Lingard and Daley Blind in front of Shrewsbury goalkeeper Jayson Leutwiler, caused controversy and confusion in equal measure.
As a result the Premier League has written to clubs this week in order to clarify that the tactics used by United should have resulted in Mata’s goal being chalked off.
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A statement read: “The Premier League has this week written to its clubs to provide guidance regarding the offside law. The guidance is in relation to players standing in an offside position when a free-kick is taken.
“Professional Game Match Officials Limited (PGMOL) issued this guidance to clear up misunderstandings that arose following the goal awarded to Manchester United in their FA Cup fifth-round tie against Shrewsbury Town on Monday night.
“PGMOL consulted the International Football Association Board (IFAB) as to whether there was an offside offence or not. As a result the PGMOL guidance below clarifies the situation.
“For the avoidance of doubt, similar scenarios in the future will be expected to be given as offside.”