Lucas was hurt in the build-up to the goal which cost Leeds a defeat at Cheltenham Town last Sunday and he is unlikely to be available for the visit of Port Vale.
Ankergren, meanwhile, required 17 stitches in the wound he suffered during United's FA Cup first-round replay defeat to Hereford United last month and the cut forced him to miss a league match for the first time this season at Whaddon Road six days ago.
Assistant boss Dave Bassett said: "Casper's progressing pretty well and we're hoping that he'll be alright for Tuesday. But it's difficult to say for certain at the moment. It's an important situation because Dave Lucas has a problem with his neck, and he looks very doubtful. With any luck Casper will be fine, but he needed 17 stitches in the cut and we have to be a little careful."
Leeds would be left without a senior keeper if Ankergren and Lucas are both unavailable. The Whites recruited Scottish youngster Alan Martin from Motherwell in August, while academy product Jonathan Lund has now recovered from a serious shoulder problem, but neither player has made a first-team appearance.
The Football League's emergency loan window closed on November 22, but the authorities may provide special dispensation for on a temporary replacement if Leeds are without an experienced option on Tuesday.