And the manager has admitted that the club are set to seek a second opinion on the injury.
There was an outside chance USA international Yedlin could return this weekend, but Benitez has ruled him out of the Championship clash.
While the initial issue was thought not to be too serious, Yedlin is still struggling. And as a result the club have decided to have the issue looked at by a specialist.
Manager Benitez refused to put a time frame on how long United will be without the pacy right-back.
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Rafa confirmed: "Yedlin is out.
"We have to wait because we want another opinion about how long it will be."