Roethlisberger hurt his throwing elbow and didn't take a snap in the second half, while Conner suffered from a knee issue. Steelers head coach Mike Tomlin had no update on either player postgame, saying only that both were being evaluated.
The veteran quarterback will undergo an MRI on Monday to determine the extent of the damage to his elbow, NFL Network's Ian Rapoport reports.
With the team's offensive stars out of commission, Pittsburgh dropped its home opener 28-26 to the Seattle Seahawks, falling to 0-2 for the first time since 2013.
"We lost a number of guys in this game, but that wasn't the reason we didn't win this game," Tomlin said. "We were fully capable with the guys that were on the field. We didn't make enough plays, to be honest with you."
Roethlisberger went 8-of-15 passing for 75 yards before leaving on Sunday, while Conner rushed for 33 yards and one touchdown on 11 carries.
Backup quarterback Mason Rudolph threw two touchdown passes and went 12-of-19 passing for 112 yards, though he also tossed an interception. He filled in for the NFL leader in passing yards from a season ago.