Brayford was an ever-present for the Rams this season until the problem ruled him out of the npower Championship fixture at league leaders Cardiff on Tuesday night.
The club continue to assess Brayford, with coach Johnny Metgod saying it remains too early to forecast how long the right-back may be out.
"It needs a scan but it's not done yet, so we'll have to see how that progresses over the next few days," Metgod told reporters on Wednesday.
"Whether it's a long-term one, it's hard to tell at the moment."
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