Stewart-Haas Racing has revealed that their driver and team co-owner Tony Stewart is in hospital with a back injury following an accident in an all-terrain vehicle on Sunday afternoon in California.

A statement from the team said that the 44-year-old three-time NASCAR Sprint Cup champion was awake, alert and able to move his extremities, but gave no indication as to where Stewart was being treated.

A report from Fox Sports said that Stewart was driving a sand buggy in San Diego when the vehicle suddenly flipped over. Stewart was airlifted to a local hospital for initial evaluation and treatment.

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The team said that it would be making no further statements about Stewart's condition until Thursday when more information would be known.

"We have received word from Stewart-Haas Racing of Tony Stewart's accident and injury," NASCAR chairman Brian France said after being informed of the news. "On behalf of everyone at NASCAR, I wish Tony a full recovery and look forward to seeing him back in our sport when he's ready to return."

Stewart had already announced that the upcoming 2016 Cup season would be his last as a driver and that he would be retiring from competition after the season finale at Homestead-Miami Speedway in November.

The decision to retire comes after a run of bad luck, including suffering a serious injury in August 2013 followed by a troubled 2014 season that was overshadowed by Stewart's involvement in the accidental death of another competitor in a regional dirt track event in New York state. Stewart slumped to a career-worst average finish in 2015, which led to the driver deciding it was time to bring down the shutters on a distinguished racing career that started in the open-wheel IndyCar Series in the 1990s.

Now the news of Stewart's accident throws into doubt his participation in the season opener at Daytona International Speedway this month. The first practice is scheduled for next week on February 12, followed by the exhibition Sprint Unlimited event the following day.

The first Cup race of the year, the Daytona 500, will take place on February 21. That means Stewart faces a tight turnaround to be ready in time to be on the grid - even assuming that his injuries allow him to be medically cleared to take part at all.

If Stewart does end up sitting out the first few events of 2016, it doesn't automatically mean that his swan song season will also be in ruins. Last year, Kyle Busch was injured the day before the Daytona 500 and ended up missing the first 11 races of the season but he still fought his way back into contention, made the Chase cut-off, and went on to be crowned Cup champion for the first time.

Twitter was abuzz on Tuesday as fellow NASCAR drivers sent Stewart their best wishes for a speedy recovery, including support from his three co-drivers at SHR - Kurt Busch, Kevin Harvick and Danica Patrick.