Maria Sharapova, the world's best-paid female athlete, has signed an eight-year extension to her sponsorship with Nike in a deal that could be worth US$70 million to the Russian.

Sharapova, who first signed a contract with Nike when she was just 11 years old, also has lucrative contracts with Tiffany, Canon and Sony Ericsson. Her existing five-year contract with Nike was thought to be in the region of US$45 million.

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The new contract will begin immediately and will also see Sharapova collect a share of profits on a line of dresses she is designing for Nike.

Sharapova counts the Australian and US Opens and Wimbledon amongst the tournaments she has won. The Russian has also been world number one twice, and has currently climbed back towards the top ten after a long-term shoulder injury.