McNamee has said he injected former Yankees and ex-Houston Astros pitcher Roger Clemens with steroids and human growth hormone.
Clemens has denied using performance-enhancing drugs.
McNamee told police he blacked out yesterday afternoon because of an ongoing medical problem.
The Daily News and New York Post report the accident happened in Queens.
Police didn't immediately release further details.
-- McNamee testified under oath before a Congressional committee that he injected Clemens with performance-enhancers at least 16 times between 1998 and 2001.
Clemens has sued McNamee -- claiming defamation.