Sweed, the team's second-round draft pick in 2008, was mounting a comeback from some emotional issues that caused the Steelers to place him on injured reserve for the final two games of last season.
If the tendon is ruptured, it likely would mean that Sweed could not play in 2010.
We don't yet know how serious Sweed's injury is, but we'll update as soon as we find out. In the meantime, here's an assessment of Sweed by our Steelers blog, Behind The Steel Curtain:
With Santonio Holmes no longer in the picture, I think Limas now has a very real opportunity at getting on the field regularly. Had Holmes been around this season, he, Ward and Wallace all would have been guaranteed significant snaps and opportunities in the passing game barring injury. Throw in Antwaan Randle El, who may not be a huge force this year, but will still get some plays designed for him, and the opportunities for Sweed to break out of his funk would again have been few and far between.
Check out the rest of the post for more on Sweed.