A diluted sample is usually regarded as a failed test under the NFL's drug-testing program.
Mettenberger's diluted sample was reported earlier Monday by ProFootballTalk.com.
Mettenberger is one of more than 10 prospects with positive tests from the combine, sources told Schefter.
FOX Sports reported that Florida State defensive tackle Timmy Jernigan, LSU defensive tackle Anthony Johnson, and Florida State linebackers Telvin Smith and Christian Jones were among the other players to fail tests. Jernigan is a projected first-round pick.
Jason Eliowitz, Mettenberger's physical therapist, said the quarterback has been drinking at least one gallon of water per day to combat dehydration, according to ProFootballTalk.com.
Mettenberger's agent, Joe Linta, said medical documentation for Mettenberger's condition was provided to Dr. Lawrence Brown, the league's adviser for drugs of abuse and alcohol. Linta told Schefter he is still awaiting Brown's response.
Jernigan's agent, Sonny Shah, told ESPN's Joe Schad that, like Mettenberger, Jernigan's test result was a result of over-hydration.
Information from ESPN NFL Insider Adam Schefter and ESPN's Joe Schad was used in this report.
Mettenberger's Draft Stock Affected?
Mel Kiper Jr. explains why former LSU quarterback Zach Mettenberger's draft stock will not be impacted greatly after he produced a diluted sample at the scouting combine.