(AP Photo/Dita Alangkara, File)

(AP) -- Roger Federer is withdrawing from this month's Miami Open so he can spend extra time preparing to "work his way back out on tour," his agent told The Associated Press on Monday.

The 20-time Grand Slam champion has not competed in more than a year after having two operations on his right knee during last season.

Federer, who turns 40 in August, is scheduled to make his return to the tour next week in a hard-court tournament at Doha, Qatar. He posted a photo of himself on Twitter last Friday with the caption: "The countdown to Doha begins."

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