LAS VEGAS — Tony Stewart still doesn’t know when he’ll be back in his car to begin his final NASCAR season.

And yes, the three-time Sprint Cup series champion says he’s still done after this year.

Stewart is hoping to return to his car quickly, but he’ll know more about his recovery from back surgery when he has X-rays next week. He defied his doctors’ wishes with a cross-country flight to Nevada this past week, although he spent most of it flat on his back.

‘‘I’m definitely breaking the rules,’’ Stewart said Friday. ‘‘But I can’t lay in bed any longer. It’s about to kill me. We did everything short of bubble-wrap me to ride out here on the plane.’’

Rest is necessary to ensure a full recovery for his broken vertebra, but Stewart wanted to support his Stewart-Haas Racing teammates and employees at Las Vegas Motor Speedway this weekend when NASCAR opens its three-race Southwest swing. Brian Vickers is driving Stewart’s No. 14 Mobil 1 Chevrolet in Las Vegas, and Ty Dillon also will drive the car in other races.

Although he isn’t following the letter of his doctors’ instructions, Stewart also won’t return to his car until his body is ready.

‘‘This is a different injury than the leg injury,’’ Stewart said, referring to his broken leg in 2013. ‘‘The leg injury was a much more severe injury, but this is a much more sensitive injury. If this doesn’t heal right, if we do something that messes it up, it could affect me the rest of my life. It’s more important to let this thing heal right. We’re not rushing to get back in the car.’’

Stewart underwent back surgery after he was injured in a low-speed dirt buggy accident near the California-Arizona border on Jan. 31.

Stewart squashed any speculation about running a limited schedule next year, shaking his head at the suggestion of a future Sprint Cup career beyond this season, lamenting the circumstances of his injury, which happened in a 25-foot drop off a sand dune at 5 miles per hour.

‘‘I’m not going to change the plan because I got hurt,’’ Stewart said. ‘‘These are the cards we were dealt.’’

Stewart hopes to get a medical waiver from NASCAR that would allow him to compete for a spot in the Chase for the Sprint Cup, like Kyle Busch did last year. Busch, winner of Saturday’s Xfinity Series race at Las Vegas, missed the first 11 races with a broken leg before winning the championship.

‘‘Whatever they decide, they decide,’’ Stewart said. “I would like to think it’s going to be similar to what they did with Kyle. The biggest thing is just getting this to heal properly.’’