Coach Byron Scott said Nash had "a little bit of a setback" earlier Wednesday while carrying bags.
Scott says Nash "heard a twinge" in his back, and the coach suspected it was a back spasm. The Lakers don't know how long the two-time NBA MVP will be out of action.
The 40-year-old Nash was able to play in just 15 games last season while struggling with nerve root irritation. The Lakers are trying to keep Nash healthy during training camp, but he hasn't practiced since asking to leave Sunday's exhibition game with an unspecified health problem.
Jeremy Lin also has a sprained ankle, but the point guard ran in practice Wednesday.
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