Citing "sources with knowledge" of Braun's drug test, SI.com said the Brewers' slugger and National League MVP showed levels of exogenous testosterone -- a banned, performance-enhancing drug -- that were likely the highest ever recorded in Major League Baseball.
The publication cited sources saying the outfielder does not hold a therapeutic use exemption from the league for prescription testosterone.
It reported Braun conducted a second, voluntary test after learning of his positive result in October. The second test, taken several weeks after the first, showed normal testosterone levels, the sources said.
SI.com said neither Braun's spokesman nor his attorney immediately returned messages asking whether Braun's voluntary test was analyzed for other banned substances as well.
Braun has strongly denied taking banned substances, and has indicated he will seek arbitration to dispute the positive test, which could result in a 50-game suspension.
The slugger may defend himself by arguing that a testing malfunction may be responsible for one test produced such an extraordinarily high testosterone level, the publication said.