Tyson joined the Rams' npower Championship rivals last week on a deal until the end of the season.
The 30-year-old made his debut for the Lions as a half-time substitute in their 2-0 home defeat to Burnley but was on the receiving end of a heavy knock shortly after his introduction.
Millwall manager Kenny Jackett revealed after Saturday's game that Tyson had damaged ankle ligaments and was worried that the player might be out for several weeks.
Tyson is set to undergo a scan on Monday to determine the extent of the injury.
- Sports & Recreation