Adrian Peterson is scheduled to have surgery today to repair the torn meniscus in his right knee, a surgery that could end the Vikings running back's season.
Coach Mike Zimmer confirmed the surgery plans at his Wednesday news conference but did not elaborate on a timetable for Peterson's return.
"I have no idea … we'll find out during surgery," Zimmer said. "It depends on if the (doctor) has to repair it or mend it. Could be season ending, could be three, four weeks, I don't know.
"Have to talk to the doctors. I'm sure they'll let us know after the surgery."
Peterson has not been placed on injured reserve.
The Vikings signed veteran running back Ronnie Hillman, who played the past four seasons for Denver, appearing in 48 games for last season's Super Bowl champions. He had 863 rushing yards last season.
The team also put left tackle Matt Kalil on injured reserve as he will have hip surgery.
ESPN reporter Josina Anderson interviewed Peterson on Wednesday and was told he has what is known as a "bucket handle tear" and could be out for 3-4 months. Peterson told Anderson he was recovering with "faith and optimism."
BRONCOS: Defensive back Darian Stewart was fined for a hit to the helmet on a quarterback for the second straight week. Stewart was fined $9,115 by the NFL for a hit on the Colts' Andrew Luck a week after being hit with a $18,231 fine for a hit on the Panthers' Cam Newton.
BROWNS: Rookie wide receiver Corey Coleman broke his hand during practice. The team didn't indicate how long the first-round pick would be out. Also, suspended receiver Josh Gordon had an arrest warrant issued against him in a paternity case.
CHARGERS: Defensive end Joey Bosa, the team's first-round draft pick, practiced in pads for the first time. Bosa missed all of training camp due to a contract dispute.
CHIEFS: Coach Andy Reid called the prognosis of Jamaal Charles "all positive," increasing the likelihood that the injured running back will get on the field this weekend. Charles has not played since Week 5 last season, when he tore the ACL in his right knee.
COLTS: Three days after taking 16 hits, Andrew Luck missed practice with a sore throwing shoulder. Luck said it was just sore and said he plans to play Sunday.
LIONS: Starting running back Ameer Abdullah went on injured reserve with a foot injury he suffered in Sunday's loss to the Titans.
SAINTS: Cornerback P.J. Williams is headed to injured reserve after sustaining a concussion last week.
TITANS: Right guard Chance Warmack will have surgery to repair a torn tendon in a finger on his right hand and is headed to injured reserve.
WASHINGTON: Wide receiver DeSean Jackson has knee and ankle injuries that could keep him out of Sunday's game against the Giants. Jackson watched practice in street clothes.