Washington, who tore his left anterior cruciate ligament against the Indianapolis Colts, and Lawrence, who injured his knee against the Cleveland Browns, were both placed on injured reserve on Tuesday.
"These are guys who are going to have special-teams impact, maybe this week or next week," Ravens coach John Harbaugh said during his weekly WBAL radio program Tuesday night. "They're also guys who have long-term value."
Williams was signed off the Tennessee Titans' practice squad.
A former seventh-round draft pick from Washburn, Williams has recorded a dozen tackles and one pass deflection this season.
Williams was a Division II All-American selection, intercepting seven passes and returning two kickoffs for touchdowns as a senior. After transferring from Fordham, he became the only player in school history to score on an interception, a kickoff return and a reception during the same season.
The 6-foot-1, 185-pounder ran the 40-yard dash in 4.43 seconds at the NFL scouting combine last year. Williams was shuffled off and on the Titans' practice squad for the past two seasons.
"Cary is an up-and-coming corner," Harbaugh said. "He's tall, he's rangy, he can run. I think Tennessee really liked him, but we had a chance to bring him in with Fabian's situation. He's developmental and I think he has a chance to help us this year, too."
Ali is a 6-foot-2, 255-pound bruising lead blocker who played in 28 games for the Cleveland Browns between 2007 and 2008.
He was cut prior to the regular season after injuring his back and suffering a concussion during the preseason before being signed by the United Football League's New York Sentinels.
Ali went undrafted in 2007 out of Arkansas Pine-Bluff where he also played linebacker and defensive end before moving to fullback. He was the only undrafted free agent to make the Browns' roster in 2007.
"Charles Ali is a 275-pound blocking type guy," Harbaugh said. "He hurt his back and had to play in the UFL and did a nice job."
Washington had 41 tackles and eight pass deflections with no interceptions.
Rookie third-round draft pick Lardarius Webb is expected to take his place in the starting lineup.
Lawrence was an important special-teams contributor, registering 16 tackles and a forced fumble this season with one reception for four yards and a long run of four yards.
NOTES: In the wake of the Ravens getting stuffed three times at the Colts' goal line during the fourth quarter of a 17-15 loss, Harbaugh acknowledged that he wasn't happy with the run blocking. "There was nowhere for Willis McGahee to go," he said. ".. We need to be a running team. We want to get those numbers up where they belong." ... After being cut by the Ravens last week, Steve Hauschka tried out for the Atlanta Falcons along with three other kickers audition for Jason Elam’s job. The Falcons also tried out Shane Andrus, Sam Swant and Brandon Coutu. ... The medical coroner ruled that former Ravens linebacker Tony Fein died of an accidental overdose. According to the Kitsap Sun, toxicology reports found that Fein died of "acute opiate intoxication," having ingested morphine and an anti-anxiety drug called Alprazolam. At the time of his death, Fein’s lawyer told the Carroll County Times that Fein committed suicide. The Iraq War veteran was arrested during the preseason at the Inner Harbor for allegedly assaulting a police officer with his agent complaining that Fein had been racially profiled. Prosecutors had told Fein's lawyer that the charges were going to be dropped, but Fein was discovered unconscious at a friend's residence one day before his scheduled court hearing. ... The Pittsburgh Steelers signed former Ravens cornerback Corey Ivy and veteran linebacker Rocky Boiman. ... The Steelers plan to sign former University of Pittsburgh quarterback Tyler Palko to their practice squad today after he clears CFL waivers from the Montreal Alouettes. When coach Dave Wannstedt stuck with Palko as his starter at Pitt, Joe Flacco opted to transfer to Delaware before being drafted in the first round by the Ravens.