The defender suffered a knee injury in last week’s 1-1 draw against Crystal Palace.
Head coach John Carver was hopeful that Dummett – who took a blow to his kneecap at Selhurst Park – had suffered nothing more serious than bruising.
But the 23-year-old is still in pain ahead of Saturday’s Premier League game against Manchester City.
The problem is still being assessed by the club’s medical staff.
And there are fears that the Wales international – who was on crutches as a precaution in the days after the Palace game – could be sidelined until April.