A former Carolina Panthers player who received what the NFL deemed a career-ending concussion has sued Lloyd's of London for denying a $US1 million ($A1.33 million) insurance policy.
The lawsuit filed this week in North Carolina could become a test case for insurers dealing with the fallout from sports concussions and head trauma claims.
The NFL has awarded defensive back Haruki Nakamura full disability benefits since the August 2013 concussion in a pre-season game.
The lawsuit says Lloyd's medical expert nonetheless found he could return to play but should consider the "probable long-term effects of repetitive concussions".
The 30-year-old Nakamura says he already has headaches, vision problems and depression.
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A Lloyd's spokeswoman says it doesn't comment on pending litigation.
A lawyer says Nakamura paid $US17,000 a year for the bodily injury policy.
