But speaking to CNN, sports business expert Simon Chadwick questioned the relevance of measuring value in this way.

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"It's simply a very nice piece of short-term brand alignment that will be mutually beneficial to both parties, " sports business expert Simon Chadwick told CNN.

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"Rather than competing against one another, Sharapova and Na actually provide Eisenbud's business with much greater global coverage, " British sports business expert Simon Chadwick told CNN.

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