Huddersfield striker Theo Robinson will have exploratory surgery on his injured knee to establish the full extent of the problem.
Robinson sustained the injury during his three-month loan spell at Millwall, where he scored two goals in six appearances for Kenny Jackett's side. The 21-year-old has since returned to the Galpharm Stadium.
Town manager Lee Clark said: "We don't know at this stage how long Theo might be out because, until the specialist has a look, we won't know the full extent of the problem.
"Here is an issue, obviously, which needs to be addressed, but we just don't know if it's a minimal thing or more serious."