Los Angeles Lakers guard Steve Nash has been ruled out for the season because of a back injury, putting the two-time NBA MVP's career in doubt.

The Lakers and Nash announced their joint decision Thursday, less than a week before the start of what would have been the 40-year-old Nash's 19th NBA season. He played in only 15 games last season with nerve root irritation, but hoped for a comeback season after several months of rehabilitation.

Instead, the Canadian point guard played in just three preseason games before feeling more back pain. He then strained his back while carrying bags several days ago.

"Being on the court this season has been my top priority, and it is disappointing to not be able to do that right now," Nash said. "I work very hard to stay healthy, and unfortunately my recent setback makes performing at full capacity difficult. I will continue to support my team during this period of rest, and will focus on my long-term health."

Nash will "focus on rest and rehabilitation," according to the team's news release. He is in the final season of his three-year contract with the Lakers, but the club's announcement made no mention of possible retirement.

Nash has played in only 65 games since the Lakers traded four draft picks for him in 2012 in a spectacularly failed attempt to assemble a title contender built around Kobe Bryant, Dwight Howard, Pau Gasol and Nash.

Nash, the NBA's oldest active player, is due more than $9 million US this season.

"As disappointed as we are for ourselves and our fans, we're even more disappointed for Steve," Lakers general manager Mitch Kupchak said. "We know how hard he's worked the last two years to try to get his body right for the rigors of the NBA, and how badly he wants to play, but unfortunately he simply hasn't been able to get there up to this point in time. Steve has been a consummate professional, and we greatly appreciate his efforts."

Third in all-time NBA assists

Nash is the greatest player in Canadian history and one of the most complete offensive guards of his generation.

He is third on the NBA's career assists list, trailing only John Stockton and Jason Kidd. Nash also is the most accurate free-throw shooter in NBA history, barely edging Mark Price's career mark at 90.4 percent.

During training camp, Nash said he realized the upcoming season likely would be his last. Yet he refused to call it a farewell tour, holding out hope of playing beyond this season if his back held up under the pounding of a full NBA schedule.

Instead, he couldn't even make it to opening night, a bitter disappointment for a dynamic competitor who hasn't won a title.

Nash won two MVP awards with the Phoenix Suns while leading one of the most dynamic offences in NBA history. His playmaking and scoring abilities have earned him worldwide recognition and eight All-Star game selections.

But Nash's tenure with the Lakers has been mostly miserable from his second game, when he broke a bone in his left leg and missed the next 24 games.

He also struggled with injuries to his hamstrings and back before last season, when he played in just nine of the Lakers' final 74 games due to recurrent pain in his back and legs.

The Lakers had hoped Nash would be their starting point guard this season, but the club also acquired Jeremy Lin and signed veteran free agent Ronnie Price. Los Angeles, which missed the playoffs last season for just the third time in 38 years, has been projected for a rough season even with a healthy Nash.