Each official Oscar statuette is 13.5 inches tall and weighs 8.5 lbs

The statuette was listed as the best director award given to Leo McCarey for the 1944 Bing Crosby film Going My Way.

Investigators were called in when McCarey's daughter said she still had all three of her father's Oscars.

They discovered the statuette was a "high quality counterfeit", using an authentic base and a fake figurine.

The top half of the statuette weighed around 1lb (450g) more than an authentic Oscar, said experts from the Academy of Motion Picture Arts and Sciences.

OSCAR FACTFILE The statuettes are made from alloy britannium They are then plated in copper, nickel silver, then 24-karat gold Each statuette is 13.5 inches tall and weighs 8.5 lbs "Oscar" was designed by MGM's chief art director Cedric Gibbons The statuette features a knight holding a crusader's sword, standing on a reel of film

Opening bids for the Oscar at Chicago-based Mastro Auctions started at $25,000 (�13,000) before the item was withdrawn.

The Academy had strict rules prohibiting the sale of Oscars, but they came into effect in 1951, making earlier awards valuable auction items.

The organisation's executive administrator, Ric Robertson, said there were indications that the person who offered the item for sale did not know it was a fake.

He added that the Academy would try to identify who made the copy and would "pursue its legal options".

Going My Way won seven Oscars in 1944, including a best actor award for Bing Crosby, whose rendition of Swinging On A Star also won the best song Oscar.

As well as his directorial Oscar, Leo McCarey received another academy award for writing the film's story.