Nathan Tyson has suffered an injury blow just days after moving to Millwall.
The striker last week joined the Lions on loan from Derby and made his debut as a half-time substitute in Saturday's 2-0 defeat by Burnley.
But he picked up an ankle ligament injury towards the end of the match and is to have a scan to determine the extent of the damage.
Whatever the result of the scan, Tyson will be a major doubt for Friday night's FA Cup visit of Aston Villa.
Meanwhile, Lions skipper Paul Robinson is set to fly out to Philadelphia in a bid to solve the injury problems which have plagued him almost all season.
The centre-half, whose last appearance was in late September, will visit a surgeon who specialises in complex groin problems.