The Pittsburgh-St. Louis kickoff was delayed when the playing field caught on fire from pyrotechnics.

The Steelers now have to hope their 2015 season isn't going up in flames following Ben Roethlisberger's knee injury.

Roethlisberger went down late in the third quarter when hit low by Rams safety Mark Barron, who had lost his balance while surging toward the star quarterback on a blitz. Roethlisberger immediately dropped the football and clutched his leg before being helped by trainers off the field. He was taken to the locker room on a cart and later left Pittsburgh's locker room on crutches.

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ESPN reported that Roethlisberger is expected to miss at least four weeks. FOX Sports NFL insider Mike Garafolo reported the Steelers are optimistic Roethlisberger avoided an anterior cruciate ligament tear that would have ended his season. The best-case scenario would be a sprained medial collateral ligament.

A magnetic resonance imaging (MRI) test is slated Sunday night for Roethlisberger when the team arrives home. Besides providing a prognosis on the status of his ligaments, the exam also will show whether Roethlisberger suffered any cartilage tears or fractures in his leg.

Roethlisberger's renowned toughness may help him get back on the field quicker than other QBs in the same situation. But even if it's "only" an MCL injury, it's difficult to envision Roethlisberger playing Thursday night against Baltimore. That short turnaround puts the Steelers (2-1) and Roethlisberger's replacement in an especially difficult position.

Mike Vick didn't enjoy the luxury of a full training camp in Pittsburgh. Having drawn scant interest in free agency, the 35-year-old Vick wasn't signed until late August after backup Bruce Gradkowski (finger) landed on injured reserve and third-stringer Landry Jones showed he wasn't ready for the job after extensive preseason playing time.

Vick's performance against the Rams can't put Steelers fans at ease. Vick completed five of six passes for 38 yards but he was sacked twice and the Steelers were forced to punt on his first three possessions.

The best thing that can be said is that Vick didn't make the same costly mistake as St. Louis quarterback Nick Foles, who was intercepted by Steelers safety Will Allen on a bad overthrow with roughly three minutes remaining.

Steelers offensive coordinator Todd Haley will probably have to scale back his game plan for the Ravens game on account of Vick's lack of experience in his system, especially with such little practice time before Thursday's matchup. There also may be some tweaking to account for Vick being a left-handed thrower.

The Steelers have faced difficult scenarios before without Roethlisberger and survived. For example, Charlie Batch and Dennis Dixon went 3-1 as starters when Roethlisberger was suspended for the first four games in 2010. That squad ended up reaching the Super Bowl.

The 2015 Steelers are different. The defense is no longer as dominant while being rebuilt and can't be relied upon to carry the load in Roethlisberger's absence. The offense is this team's strength.

The fact Vick is now surrounded by the best skill-position talent of his 13-year NFL career could help him reverse what has been a four-season slide. The Steelers also can rely more on their rushing attack with Le'Veon Bell now back from his two-game drug suspension to team with DeAngelo Williams.

But such talk is optimism. This is reality: The Steelers aren't in the championship mix unless Roethlisberger is playing sooner than later with Cincinnati (3-0) poised to run away with the AFC North.