He joins as part of the deal that sent Louis Saha to Tottenham.
Pienaar left Everton for Tottenham last summer, but like many signed by Harry Redknapp soon found himself out of favour.
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Who of Europe’s top strikers will move to England this summer?
After a dreadful start to their Bundesliga campaign, Borussia Dortmund appear to have weathered the storm after going five matches without defeat.