Quinn will be eligible to return to game action Sept. 22 against the Miami Dolphins, who traded him to the Cowboys in March. On Wednesday, Quinn had surgery to repair a fractured left hand suffered in Tuesday's practice, and the team believed he would be ready to play for the Sept. 8 season opener against the New York Giants.
Quinn's agent, Sean Kiernan, released a lengthy statement defending his client, saying they believe his preventative anti-seizure medication was contaminated with the probenecid of someone else's prescription, which was filled at the same pharmacy just before his.
"Rob has a medical history with seizures that requires him to take multiple doses of preventative medication daily to regulate them," Kiernan wrote. "He was tested on April 2nd under the NFL Steroid Policy. He failed the test for a substance called probenecid, which is classified as a masking agent under the policy. He does not take any supplements and took nothing else during this period that would create a positive test for probenecid, in fact, he had no idea what probenecid was or what it was used for."
Kiernan also took exception to the league's tactics during the hearing process.
"I've been working with NFL Players for 20 years, and I can't think of a situation where I've been personally involved where the league was as tone deaf as it was here," he wrote. "Now, Rob will be punished for something that would have been impossible for him to prevent, and even though the NFL admitted during the hearing that it did not believe Rob was intentionally doping, they still suspended him. The arbitrator gave us a fair hearing, but the strength at which the league argued against Rob was incredibly disappointing."
Before the suspension was announced, Quinn had his appeal denied by an independent arbitrator selected by the NFL and NFL Players Association. Under the PED policy, a player is subject to a two-game suspension if a masking agent is found in testing.
Coach Jason Garrett said the team is 100% behind Quinn.
"We support Robert Quinn. We trust Robert Quinn," Garrett said. "We really like everything he's done for our team since he's been here. We're excited about his future with our team."
Garrett said the Cowboys became aware of the possibility of a suspension in the past few weeks. Quinn is expected to return to the Cowboys on Sunday to begin his rehab on his left hand and continue conditioning work.
With Quinn out for the first two games, it creates some potential roster issues for the Cowboys when the final cuts are due and opens opportunities for other players, like Taco Charlton, Dorance Armstrong and Kerry Hyder.
Randy Gregory has yet to file for reinstatement from his indefinite suspension, and DeMarcus Lawrence (shoulder) and Tyrone Crawford (hip) have opened training camp on the physically unable to perform list.
The expectation is Lawrence and Crawford will begin practicing when the Cowboys return to Frisco, Texas, after their Aug. 17 preseason game against the Los Angeles Rams in Honolulu.
The Associated Press contributed to this report.