Alex Ferguson (AFP)

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London - The English Football Association has asked Manchester United manager Alex Ferguson to explain why he criticised a referee's assistant following Sunday's 1-1 draw at Tottenham.

Ferguson was angry that linesman Simon Beck didn't award a penalty in the second half after Wayne Rooney tangled with Steven Caulker, with United leading 1-0.

Ferguson claimed in a television interview that "there was no way we were going to get a decision from" Beck, citing a 2010 decision to allow a goal by Didier Drogba to stand for Chelsea at United when the manager claimed the striker was offside.

Ferguson has until Thursday to clarify his comments after being contacted by the FA.

The Scotsman, who has faced several previous sanctions for criticising referees, could be charged with misconduct if the FA rules he questioned Beck's integrity.