As the Texans are being nonspecific as to damage to "what" cartilage, one of the "better" scenarios (and it's still no bargain), is the cartilage involving the back side of the patella (knee cap).....patellar chondromalacia......where it is essentially crushed many times with damage to the apposing cartilage of the femur surface of the knee joint behind it. The deeper the bone bruise, the greater the probable cartilage damage to both surfaces. The more subsequent movement allowed, the greater damage is created by the two surfaces "grinding."
Adequate rest is again absolutely necessary after such a "clean up." Then intensive rehab. Depending on the extent of damage, I would still be surprised if return should take any less than a couple of months.....and with greater damage greater potentially many more. Unfortunately, that type of surgery does not correct the problem (cartilage is gone).........and the player may very likely still show progression to more severe problems with quickly decreasing levels of performance. Bone on bone and severe arthritis is commonly the final end results, with some players never coming back.