The 31-year-old limped out of the weekend´s friendly clash with Sampdoria and has been sent for further assessment after being dogged by similar problems for much of last term.
"He has gone to see a specialist in London because we want to make sure just how much damage has been done," Allardyce said. "He has been for a scan and it doesn´t look serious, it´s just a slight strain. At the moment we only expect him to be out for a couple of weeks, but we won´t take any risks."
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