Ashburn, VA -- (Sports Network) - Clinton Portis heads a list of eight players who were unable to practice on Thursday leading up to Washington's road test in Baltimore on Sunday versus the Ravens.

The seventh-year pro has been dealing with a nagging knee sprain he suffered during the Redskins' loss to Pittsburgh on November 3 and is now also dealing with a back injury.

Portis has been on the injury report nearly every week since his knee sprain but continues to suit up come game-time, often with good results. However, Portis was held to a paltry 22 yards on 11 carries with one catch for 15 yards in last Sunday's 23-7 loss to the New York Giants.

Portis is the second-leading rusher in the NFL this season with 1,228 yards. Only Minnesota's Adrian Peterson (1,311) has more. Portis has also rushed for seven touchdowns, and caught 23 passes for 187 yards.

Starting left tackle Chris Samuels (knee) also missed practice, while Washington's defense continues to be racked with injuries.

Defensive end Andre Carter (foot), linebacker London Fletcher (foot), defensive tackle Kedric Golston (ankle), cornerback Shawn Springs (calf), linebacker Marcus Washington (ankle) and cornerback Fred Smoot (non-injury) all did not participate Thursday.

All but Smoot are a part of Washington's regular starting defense.