METAIRIE, La. -- New Orleans Saints running back Mark Ingram "vigorously challenged" his four-game suspension, according to a statement from his agents, saying that he tested positive for a substance that was "permissible with the proper use exemption with the NFL."

The NFL, however, reiterated Wednesday that an arbitrator has made a final ruling on Ingram's appeal, which is why the league announced his suspension on Tuesday.

Ingram's agents suggested in their statement that they might explore further options once they review the arbitrator's full opinion, which is due by May 16. But NFL spokesman Brian McCarthy clarified that the outcome has been decided and that all parties have been notified. The only thing they are waiting on is the full written explanation, and there is no further appeal still to be decided through the NFL.

Neither side has specified which substance Ingram tested positive for. The NFL announced only that he violated the league policy on performance-enhancing substances.

"At the end of the 2017 season, as a result of a NFL mandated random drug test, Mark Ingram tested positive for a substance that was not a performance enhancing substance, nor an illegal substance, but a substance in fact permissible with the proper use exemption with the NFL," Ingram's agents, Paul Bobbitt and David Jones, said in the statement.

"He has vigorously challenged the test results through the arbitration process. ... Upon having the opportunity to review the arbitrator's opinion, we will explore what further options are needed."

If the suspension stands, Ingram will miss games against the Tampa Bay Buccaneers, Cleveland Browns, Atlanta Falcons and New York Giants. He will be eligible to return to the Saints' active roster on Oct. 1.

Ingram, 28, made his second Pro Bowl by running for a career-high 1,124 yards and 12 touchdowns. He also caught 58 passes for 416 yards.