McAlister, a two-time Pro Bowl defender who was benched two weeks ago, did not practice yesterday after receiving a second opinion on his knee injury by a specialist in Miami.
Ravens coach John Harbaugh said the injury could require surgery and could "potentially" result in McAlister's being put on injured reserve, which would end his season. A decision could be made by the end of the week.
"It's really between the doctors and Chris to make a decision about what's best for Chris going forward this year and for the rest of his career," Harbaugh said. "We're really hopeful that he'll play for us this year."
With McAlister likely out, the Ravens could see the return of cornerback Samari Rolle, who has missed the past five games with a neck injury. Harbaugh said there is a "good chance" Rolle will play for the first time since Sept. 21.
"I think we just need to see how he goes through practice and how it responds, how he feels after a good hard practice," Harbaugh said. "It could go up to game time to make a decision. But we're hopeful."
Meanwhile, Williams will have season-ending surgery to repair a bone spur underneath his Achilles tendon.
It's an injury Williams has battled since June. He didn't practice last week before catching a 70-yard touchdown Sunday, when he seemed to pull up after crossing into the end zone.
"We tried to work it and hoped that it would improve," Harbaugh said. "It's just not getting any better."
To fill Williams' roster spot, the Ravens signed wide receiver Terrance Copper, who was released for the second time in 12 days by the New Orleans Saints. Copper's strength is more on special teams than as a receiver.
The Ravens' other options to fill Williams' void as the No. 3 receiver are: Yamon Figurs, who returned to practice yesterday after the swelling went down in his knee, and rookies Marcus S mith and Ernie Wheelwright.
"We've got a lot of options in there," Harbaugh said. "Whatever guy or combination of guys give us the best chance will be active and will be playing."
Offensive lineman Adam Terry was expected to be sidelined for at least two weeks after undergoing arthroscopic surgery on his right knee.
But he returned to practice after missing one game and seemed optimistic about playing. Terry, who started the season at right tackle, might move to right guard.
The knee "feels pretty good," Terry said. "Now it's a case of how does it feel banging against people?"
Terry was among seven Ravens who were limited in practice: Rolle, Figurs, linebacker Brendon Ayanbadejo (ankle), offensive tackle Jared Gaither (neck), tight end Todd Heap (neck) and cornerback Frank Walker (thigh).
Strong safety Dawan Landry (neck) was declared out. McAlister, running back Willis McGahee (knee) and tight end Daniel Wilcox (thigh) did not practice.
With all the new trick plays in the Ravens' offense, receiver Derrick Mason was asked whether he could throw. Off to the side, quarterback Joe Flacco chimed in, saying with a smile, "I catch better than he throws." ... Even though he has made five straight field-goal tries, Matt Stover isn't exactly looking forward to playing at Cleveland Browns Stadium, which he considers one of the toughest places to kick. "The field conditions can play havoc on you," he said. "In November, we'll have to see what they're like." ... The Ravens have recorded an interception in eight straight games against the Browns.
Baltimore Sun reporter Edward Lee contributed to this article.