The Tennessee Titans running back is yet to rush for over 100 yards in a game this season, and has not scored a touchdown in 2013.
The 49ers linebacker told reporters: "You know, I'm not sure what's going on, his situation over there. I just know as far as what I've seen on the film that he's a guy that you might stop him nine times, but on that tenth run, he's boom, he's gone, and it's a long one.
"So, it's just one of those things you really have to hold him for as long as you have to on the field because any given moment, he can be in the end zone. For us, I don't really care what he's done up to this point, I just know we just got to make sure we don't let him get off this game."
The Titans have a 3-3 record so far this season.