6. Kleberson
The Brazilian arrived for £6.5m as a World Cup winning midfielder but, just 20 league appearances later, left an utter flop. The midfielder was injured in his first game for United to be fair, but never looked up to scratch. A disturbing reference on his wikipedia page also alludes to his desire to marry a 15-year-old shortly before joining United, but the less said about that the better.
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