The Steelers will wait for results of an MRI on Ben Roethlisberger's left knee after the three-time Pro Bowl quarterback was carted off the field in the third quarter of Sunday's 12-6 win at St. Louis.
Michael Vick replaced Roethlisberger, who got hurt when his leg was caught underneath him on a diving, sliding sack by Mark Barron. Big Ben left the stadium on crutches and wearing a bulky brace.
Steelers coach Mike Tomlin said he won't have an update on the extent of Roethlisberger's injury before Monday.
"I was kind of stunned," Vick said. "You never want to see a guy like Ben go down."
Roethlisberger hasn't missed a start since 2012, when he was out for three games late in the season because of a shoulder injury. Vick completed 5 of 6 passes for 38 yards in relief.
The Steelers (2-1) host the Baltimore Ravens (0-3) on Thursday night.
Later in the day, Seattle running back Marshawn Lynch left a 26-0 win over Chicago at halftime with a hamstring injury. Lynch finished with 14 yards on five carries and spent half of the first quarter in the locker room before coming to the Seahawks bench. Lynch was questionable entering the game with a calf injury.
"We've checked it all out and it's nothing to be alarmed by," Seahawks coach Pete Carroll said.
In other injury news:
__ Philadelphia right guard Andrew Gardner left the stadium on crutches and wore a boot on his injured right foot. Safety and special-teams ace Chris Maragos also got hurt in a 24-17 win over the Jets. He didn't return because of a left knee contusion.
__ Jets cornerback Darrell Revis tweaked his hamstring and wasn't on the field for the final plays when the Eagles ran out the clock. Revis started the game despite being questionable because of a groin injury. Right guard Willie Colon left after halftime with a knee injury.
__ Jaguars safety Josh Evans didn't return after injuring a knee in a 51-17 loss at New England. Wide receiver Marqise Lee also left in first half with a hamstring injury, and safety Sergio Brown went out with a calf strain.
__ Chargers left tackle King Dunlap (concussion), left guard Orlando Franklin (right ankle), center Chris Watt (groin) and cornerback Jason Verrett (foot) were hurt in a 31-14 loss at Minnesota. None of them returned to the game.
__ Vikings cornerback Xavier Rhodes suffered a head injury in a scary collision with teammate Andrew Sendejo in the second quarter of their win. He didn't return to the game. Defensive end Justin Trattou (left ankle) and wide receiver Charles Johnson (ribs) also didn't finish the game.
__ Falcons tight end Jacob Tamme left in first half with head injury in a 39-28 win at Dallas.
__ Browns linebacker Craig Robertson was helped to the sideline with a left leg injury in the third quarter of Cleveland's 27-20 loss to Oakland. He didn't return.
__ Titans fullback Jalston Fowler injured a left leg trying to score the tying 2-point conversion in the final minute of a 35-33 loss to Indianapolis. Fowler scored on a 1-yard run before he was stopped for a huge loss on the conversion.
__ Panthers defensive end Charles Johnson injured his hamstring and running back Jonathan Stewart hurt his leg in the second half of a 27-22 win over New Orleans.
__ Bills wide receiver Sammy Watkins missed the last three quarters of a 41-14 win at Miami after injuring his right calf.
__ Seahawks defensive tackle Brandon Mebane suffered a groin injury in the first quarter and did not return against the Bears.
__ 49ers tight end Vernon Davis injured a knee. Coach Jim Tomsula didn't know the extent of the injury after San Francisco's 47-7 loss to Arizona.
__ Bears defensive lineman Will Sutton injured a biceps and offensive tackle Jermon Bushrod suffered a concussion against Seattle.