An adviser to Tom Zbikowski says the Baltimore Ravens safety is disputing a positive drug test administered after a weekend boxing match in Oklahoma.

Zbikowski fought Saturday at the WinStar World Casino in Thackerville, knocking out Blake Warner of Oklahoma City in the first round and improving his record to 4-0.

Sixteen fighters underwent drug tests and five of them came back positive. A tribal spokeswoman says the Chickasaw Nation Gaming Commission suspended those fighters for 45 days.

Zbikowski's manager, Mike Joyce of Chicago, says he's been told Zbikowski tested positive for traces of a substance found in marijuana.

Joyce says Zbikowski took another test Tuesday at a Chicago lab and it came back negative. Joyce says Zbikowski has never tested positive for banned substances.