Venus Williams withdrew shortly before her opening match at the ATP-WTA Madrid Masters and was replaced by Swiss Stefanie Voegele.

Williams, a 2010 finalist at one of the last clay tune-ups before the May 26 start of the French Open attributed her decision to back pain. She had tweeted in recent days that her practice sessions had been very limited, giving no further details.

The 32-year-old lost in the second-round in Madrid a year ago to German Angelique Kerber.

Voegele, ranked 56th, will play against Spain’s Anabel Medina Garrigues.

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