The Minnesota Vikings have already lost their starting quarterback for the entire 2016 NFL season, and now the team waits to hear news on their star running back. Adrian Peterson left Sunday night’s game against the Green Bay Packers with a right knee injury, unable to walk back to the locker room under his own power.

When Peterson was seen hobbling off the field in the third quarter, there were fears that he might have a season-ending injury. The former MVP will undergo an MRI on Monday to determine if there is any structural damage, but Minnesota is optimistic that Peterson will be back on the field this year.

Vikings head coach Mike Zimmer indicated that the injury appeared to be worse than it actually was.

“He might miss a week. I don’t know if he will or not,” Zimmer said after Sunday’s 17-14 win over Green Bay. “Whatever it was has calmed down now, so we’ll see.”

A torn ACL would keep Peterson out until next year, and he suffered that exact injury in his left knee towards the end of the 2011 season. Even if Peterson suffered a minor knee injury, NFL head team doctor David Chao believes the running back will miss two weeks in a best-case scenario.

Prior to leaving Sunday’s game with an injury, Peterson barely had any success on the ground, totaling just 19 rushing yards on 12 attempts. Coupled with a poor performance in Week 1 against the Tennessee Titans, Peterson is off to one of the worst starts for any running back in NFL history, averaging 1.6 yards per carry.

Peterson led the league with 1,485 rushing yards a year ago, and many of his problems can be attributed to Minnesota’s offensive line. He’s gained an average of just 6.9 inches before getting hit by a defender on his 31 carries this season.

If Peterson is out for an extended period of time, running backs Matt Asiata and Jerick McKinnon will split time in Minnesota’s backfield. They haven’t done much better than Peterson this season, combining to rush for 35 yards on 13 carries.

Minnesota won the NFC North in 2015 on the strength of their running game and defense, but the team has gotten off to a 2-0 start without much help from Peterson. The Vikings scored two defensive touchdowns in the season opener, and quarterback Sam Bradford had a 121.2 passer rating in his debut with the team on Sunday.

Quarterback Teddy Bridgewater suffered a season-ending injury in training camp when he suffered a torn ACL and dislocated his knee.

Adrian Peterson Minnesota Vikings Adrian Peterson sits on the field as trainers tend to his knee in the third quarter against the Green Bay Packers on Sept. 18, 2016 at U.S. Bank Stadium in Minneapolis, Minnesota. Photo: Getty Images