Darwin Nunez scored in the 99th minute for Liverpool's 1-0 win - but only after the game had been stopped for a head injury suffered by Ibrahima Konate.
When the game restarted, Liverpool were given the ball, even though Forest had possession when referee Paul Tierney had stopped play.
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Clattenburg said: "As a club Nottingham Forest have felt one or two decisions that have gone against the club; Newcastle United, West Ham (results).
"Clear decisions where the Premier League and PGMOL have accepted that it is a mistake, today is another example where the law is quite clear.
"The law states that if the referee is going to stop the game, which he is entitled to do for an head injury, if there is a head injury.
"However, the ball has to go back to the team which has the possession and Nottingham Forest had the possession."