I just checked www.nhl.com, and apparently Erik Johnson has torn his ACL and suffered a tear in his MCL. I don't know what the difference is between tearing, and suffering a tear, but that's what it said on the St. Louis website.
Either way, this is a major loss for St. Louis, who relied heavily upon Johnson last season as a 19-year-old rookie. Johnson tallied 5 goals and 33 points last season, but also had a -9 rating. That no doubt would have, and still will, improve as the seasons go on, but this year was a key developmental year for Johnson, and he'll have to work hard to make sure that this injury doesn't affect his career permanently.
Part 2 of the "Who will be the next Darren Helm?" series comes out tomorrow, probably.