The left-back was sent to see a specialist prior to United's recent League One game at MK Dons, having failed to overcome the injury he sustained on the first day of the season, but he appeared to be on the verge of a full recovery after featuring for an hour in a behind-closed-doors game against York City last week.
Simon Grayson, however, confirmed that Parker would not be considered for selection at Elland Road this evening, saying: "Ben's had a setback again and we need to assess that. He won't be involved."