Morency suffered an injury to his lower back toward the end of the 31-14 victory over Arizona.
Head coach Mike McCarthy said Morency, a second-year player, will be out at least two weeks.
"We're going to run some more tests," McCarthy said Monday. "They're still diagnosing it. It will be with one of his disks."
Morency, whom Green Bay acquired in an early-season trade with Houston, rushed for a career-high 101 yards on only 11 carries in a complementary role. He spelled Ahman Green as a change-of-pace back. Green amassed 106 yards on 21 carries.
Green and Morency became the first pair of Packers to run for 100 yards in the same game since Eddie Lee Ivery and Gerry Ellis in 1985.
Green Bay racked up a season-best 203 rushing yards.
The Packers (3-4), riding high with two straight wins, play at Buffalo on Sunday. They will have to make do with Green and third-down back Noah Herron coming out of the backfield. McCarthy said the team could be in the market to add a running back.
"I'm more disappointed for 'Mo' because I think you're seeing him get very comfortable with our run game," McCarthy said. "He's been excellent on special teams. He's a good football player. He's a tough guy, very explosive. Unfortunately, this is part of the game. It's an opportunity for Noah to step in there."
McCarthy is hopeful that Herron, also a second-year player, can pick up the slack in Morency's absence so the offense won't have to be more reliant on Green. McCarthy has been careful since Green returned from a hamstring injury two games ago to limit his carries to about 20 a game.
Green had 18 carries for 118 yards, including a 70-yard touchdown, in the Oct. 22 win at Miami.
"We need to be conscious of that," McCarthy said. "I don't know if (running him so much) was a mistake earlier in the year, but he looks very strong where he's at with his carries.
"If he gets three or four or five more, I'm OK with that. I don't think we need to be getting into the 25- or 30-attempt type games."
Herron replaced a fumble-prone Morency early in the Oct. 8 loss to St. Louis and responded with a career-high 106 yards in 20 carries with a touchdown.
Fullback may not play against Bills
At the same time head coach Mike McCarthy was pronouncing No. 2 halfback Vernand Morency out for at least two weeks because of a back injury, he didn't have encouraging news about top fullback Brandon Miree.
McCarthy said Miree would be doubtful for Sunday's game at Buffalo because of a hyperextended left elbow sustained a day earlier in the 31-14 win over Arizona.
Miree had a productive game. He paved the way as the lead blocker for the Packers' season-high 203 rushing yards and had four catches for 31 yards, including a 20-yard grab downfield.
Veteran William Henderson, whom Miree replaced in the starting lineup in Week 4, will be back in the lead role. McCarthy doesn't anticipate a drop-off with the blocking in the running game with Miree likely out Sunday.
"It speaks a lot when you have two fullbacks and four tight ends on your active Sunday roster. We'll just go right ahead with William in there and move forward," McCarthy said.
-- McCarthy said No. 2 receiver Greg Jennings will be questionable for the upcoming game.
The rookie was deactivated Sunday because of a sprained ankle. He hasn't practiced since suffering the injury Oct. 22 at Miami.
"We worked him out Sunday morning before the game. He's close," McCarthy said. "We'll have a better idea for him on Wednesday. I'm hopeful he'll go."
-- WR Donald Driver hurt an ankle late in the victory over Arizona on Sunday, but head coach Mike McCarthy said the injury is minor. Driver returned to the game shortly after hobbling off.
-- CB Charles Woodson was further checked by the medical staff Monday after suffering an injury to his left knee early in the game Sunday. Woodson returned, so the injury isn't considered serious.
-- TE David Martin took a shot to the jaw toward the end of Sunday's game, but McCarthy said he would be fine.
-- DT Cullen Jenkins might be cleared to return to practice later this week. Jenkins has missed the last two games because of a bruised ankle.
-- LB Ben Taylor figures to be ready for the game Sunday at Buffalo. The backup and special-teams ace was held out the last three games because of a hamstring injury.