(AP Photo/Michel Euler, File)

(AP) -- Welcome back to Paris, Serena Williams. The tennis world can't wait to find out exactly how that bothersome left knee is holding up.

Williams practiced at the French Open's redesigned main stadium on Monday - alas, Court Philippe Chatrier's retractable roof won't be ready until next year - and will want to get some more work in over the coming days, given how little she's played on clay courts lately.

As in: a total of just one match on the surface since last year's tournament at Roland Garros. Forever, it seems, Williams has been the woman to beat on the Grand Slam stage, provided she is in the field and is healthy. No one really knows this time just how ready she is.

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