Portis and Betts continue to battle through injuries, but the Redskins apparently felt they needed Alexander's roster spot to help with depth on the defensive line.
The Redskins replaced Alexander on the roster by signing defensive tackle Ryan Boschetti. Defensive end Andre Carter and defensive tackle Kedric Golston both suffered foot injuries, and defensive tackle Cornelius Griffin hurt his shoulder in Sunday's 20-17 victory over the Seattle Seahawks.
Alexander spent his first eight NFL seasons with the Seahawks, leading the team to the Super Bowl after the 2005 season. He has 9,453 rushing yards and 100 career rushing touchdowns.
Alexander was looking to make a comeback after foot and wrist injuries ruined his last two seasons and prompted the Seattle Seahawks to cut him in April. However, in his limited carries with the Redskins, the 31-year-old back never showed anything close to the form that helped him rush for 1,880 yards in his 2005 MVP season.
He didn't play at all in Sunday's 20-17 win over the Seahawks, even though he was returning to the stadium where he earned his fame as well as his fortune -- in the form of an eight-year, $62 million contract signed after his MVP year.
Boschetti played 19 games with two starts for the Redskins from 2004 to '07. He was among the final cuts at the end of this year's preseason.
Mike Sando covers the NFC West for ESPN.com. Information from The Associated Press was used in this report.