UPDATE II: Jason La Canfora with CBSSports.com also writes that there was no ACL tear.
UPDATE: There are conflicting reports regarding Sunday's results from the MRI on DeCastro's knee. ESPN NFL Insider Adam Schefter tweets that DeCastro's anterior cruciate ligament in intact, though he also suffered a dislocated his knee cap and some damage to the patellar tendon, along with the MCL tear.
NFL Network's Ian Rapoport filed an entirely different report, citing a "source with knowledge of his condition", that DeCastro tore his ACL against the Bills, along with his previously reported torn MCL.
Pittsburgh Steelers rookie offensive guard David DeCastro left Saturday's game against the Buffalo Bills on a cart during Pittsburgh's second possession in the first quarter. After the game head coach Mike Tomlin said that "It's potentially severe. But we'll see what the MRI says." ESPN NFL Insider Adam Schefter tweets Sunday morning that DeCastro has a torn MCL, which could mean he could return midway through the season. However the team hasn't determined any injury to the ACL, which, combined with the MCL, would likely mean the end of DeCastro's rookie season. There's an MRI scheduled around lunch on Sunday to determine if the ACL is torn.
At last report DeCastro's training camp hasn't been taking the world by fire, struggling to breach the starting lineup until Willie Colon suffered a sprained ankle. Ramon Foster moved to left guard replacing Colon and DeCastro filled in at right guard.
Pittsburgh was on their own six-yard line with 11:49 remaining in the first quarter on third and eight. An intense pass rush from Marcell Dareus forced DeCastro back when another Steelers offensive lineman, Marcus Gilbert, accidentally impacted the back of DeCastro's right leg.
His leg gave out and DeCastro began clutching his knee as Roethlisberger threw an incomplete pass to running back Chris Rainey.
When watching most plays that result in a major ACL injury, they seem characteristic of an impact from the side, not the back. Regardless DeCastro will be out for a period of time, at least the first half of the season under the best scenario at this point.