12:37 PM ET

Chase Young will be out at least the season opener because of a knee injury.

Rivera said on Tuesday that Young would take the most time to be placed on the disabled list. According to one source, Young would return in September.

Rivera gave a timetable for Young for the first time on Thursday. Young tore his knee.

Rivera said at one point that Young would miss at least four games because he would open the season on the injured reserve list.

There is no set number of practices that players need to participate in before they return.

Rivera said he only knew that Young wouldn't play. There is a chance he would be on the injured reserve. If he went on IR, he would miss four games.

Depending on where he is. Rivera could not tell you. Only the doctor can tell you.

I'm going to give you a number." I'm not able to give you a number. I don't want the young man to be pressured to hit a number that I can't give him.

Young needed to have a knee transplant. His recovery time was extended.

Rivera said it was serious. He's doing what he's supposed to. We can update you as he gets better and the doctors think he should be. Right now, he is where he needs to be.