Tom Cable confirmed that Trevor Scott has an ACL injury. They have yet to place him on IR, but that is the likely destination for him. While Scott will be missed, it shouldn't be that hard to fill in his gap. Matt Shaughnessy will take his place in the starting line up. Shaughnessy was already playing as big of role as Scott on the D-line and by my estimation he is a superior all around defensive end.
Where this is really going to be felt is in passing situations. Typically, the Raiders would use Scott and Kamerion Wimbley on passing down DEs. The Raiders are not going to play Shaughnessy every snap and 2nd and 3rd and longs are still a good spot to spell him.
Lamarr Houston is getting better by the week, but he is not the pass rushing DE this team wants on those passing downs. So, the Raiders can either slide Groves into that pass rushing DE slot. A position he is familiar with and will also be available to focus on with the emergence of Travis Goethel. Or they can sign a FA DE. In the likely event that Scott goes to the IR, look for the Raiders to add someone. Who or how effective this guy will be is yet to be determined.