It certainly didn't look good.
The initial prognosis, as reported by Pro Football Talk, makes it almost seem worse than it looked, which says a lot.
Rookie LB Sean Spence suffered what PFT reported is a torn ACL, LCL and dislocated knee cap in Pittsbrgh's 17-16 win over Carolina Thursday, coming down awkwardly after being blocked in pursuit of Panthers QB Jimmy Clausen. (Editor's note: I linked the wrong story earlier, I apologize, PFT's story was current as of Thursday evening, and the link is now pointing to the correct story)
If that that is confirmed, it will certainly end his rookie season before the start of the real games.
It's really unfortunate because Spence looked outstanding in extensive action throughout the game. Injuries have depleted the Steelers of LBs, Stevenson Sylvester, James Harrison and Jason Worilds already, so Thursday's preseason finale was played extensively by back-ups.
Spence paid the unlucky price, but there really wasn't anyone else available. Sylvester will probably need another week before returning to the field, and Harrison and Worilds were taken off the PUP list just a few days ago.
With final cuts due at 9 p.m. Friday, the Steelers are in a bind. Choosing their 53-man roster seems like a task they'll have to repeat a few times in the next few days. LB Mortty Ivy, a victim of the initial cut, reportedly had a hamstring injury, but it wouldn't be surprising to see the Steelers give him a call to see how it's doing.