The linebacker sustained a hamstring injury last month, preventing him from playing in the team's pre-season games.
The head coach told reporters: "The thing I'm concerned about obviously is some guys that we're counting on huge have missed time. It goes back to Whitney. Whitney is back to work [yesterday]. Worked with the team, looks great. But the fact is he hasn't had a pre-season.
"Hopefully it doesn't hurt him at all. There is nothing we can do. He gets the hamstring early in camp. If you bring him back too soon, then you can lose him for a long period of time.
"Let's make sure we have him ready to go against San Diego. A lot of it is up to him. He's been working hard."
Mercilus made 25 tackles and six sacks for the AFC South side in 2012.