"I thought he was done for the year the way he fell," receiver and kick returner Antonio Chatman told The Green Bay News-Chronicle. "It looked like his leg got caught up in the turf (as) he just tried to run forward.
"It was a freak accident. I thought he blew (out) his Achilles' (tendon), but he didn't."
Receivers coach Ray Sherman, however, was optimistic Ferguson could play Sunday at Detroit.
"I'm not counting Fergy out, though, because he's always a guy that finds a way to get back in the lineup," said Sherman.
On the positive side, big-play receiver Javon Walker, who leads the NFL in receiving yards, practiced Thursday after sitting out Wednesday with a sprained right hand that has bothered him since the preseason. Chatman practiced again after dislocating his right pinkie finger during the Giants game.
Cornerback Michael Hawthorne, meanwhile, spent much of Thursday's practice at receiver for the second straight day. At 6-foot-3, he's an intriguing possibility, though he's probably not ready to make the transition in a game, Sherman said.
"I don't know if we can get him ready for this game. There's some things he can do, but it really would be a crash course," Sherman said.
Other comings and goings included:
Quarterback Brett Favre was given the day off so he could be with his wife, Deanna, who is sick, according to a team spokesman. Favre has missed practice in the last couple weeks for his brother-in-law's funeral and to clear the cobwebs after suffering a concussion.
"We like to get him as many reps as he can on the stuff that we're doing in the game plan," said quarterbacks coach Darrell Bevell. "But with his experience and the things that he's done, he's able to miss it and not miss too much."
Offensive coordinator Tom Rossley, a day after undergoing angioplasty to clear a clogged artery in his heart, spent some of the day at team headquarters before going back home. Bevell said Rossley is feeling good.
"He's a competitor and a driven guy. I'm sure that he wouldn't want to miss (the game) for anything," Bevell said. "But I don't know how much of it is in his hands. He has to be smart about it."
If Rossley doesn't make the trip, head coach Mike Sherman will call the plays.
Defensive tackle Cletidus Hunt was absent for the second consecutive day to attend his grandmother's funeral. Hunt was expected to practice Friday.
Running back Ahman Green and linebackers Na'il Diggs and Hannibal Navies, all listed as probable, practiced Thursday. Green (Achilles) took Wednesday off while Diggs (neck) and Navies (shoulder) practiced for the second consecutive day. Navies was held out of Monday's Titans game.
"That's the plan," Jackson, who's been sorely missed by the Packers' woeful defense, told the Milwaukee Journal Sentinel. "I thought I could do it quicker but you've just got to take it step by step. You try not to come back too quick and not have a season-ending surgery."