Wozniacki's injury continues a difficult season for the Dane, who was dumped from the opening round of the Australian Open and has now slumped to 34th in the rankings.
She suffered another ankle injury last month, forcing her to pull out of the Istanbul Cup tournament and a Fed Cup tie.
Bencic has also had a tough run, losing opening round matches at four of her last five events since the 19-year-old made the final at St Petersburg in February.
(Reporting by Ian Ransom; Editing by Peter Rutherford)
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