"I know he's going to talk to Dr. Anderson, but it's really not looking good [...] we'll probably announce something soon"
The doctor Rivera is referring to is Dr. Robert Anderson, a Charlotte-based physician, and the pre-eminent expert on foot injuries in the NFL. If a player is going to see him it normally isn't good, and based solely on anecdotal evidence and past experience it would be stunning to see him return this season. Pair this with Rivera calling the prospect of a season without Kalil as 'scary', and it doesn't make for an optimistic situation.
The Panthers' head coach is right-- it is scary. If Carolina are to be without Kalil for an extended period of time they'll need to rely on Jeff Byers, who has been terrible, or Geoff Hangartner which opens up a scary hole at right guard. The only other player on the roster with experience was Mike Pollak, and he hit IR last week.
In these situations it's normally wise to preach patience, and to see that things may not be as bad as expected. In this case it is absolutely fine to expect this to be a disaster. Thus far the offensive line has been inconsistent at best, and Ryan Kalil is the Panthers best offensive lineman. Fans should re-watch that week two victory over New Orleans, because it might be the last Panthers win they'll see in a while.