"I'm extremely sorry that I failed to check with the NFL, NFLPA, or Chiefs medical team before I took a medication that requires a therapeutic use exemption," Stephenson said in a statement Friday. "The rules are strict, and without a TUE, the consequence is a four-game suspension.
"I apologize to the Hunt family, [GM] John Dorsey, Coach [Andy] Reid and his staff, my teammates, and our awesome Chiefs fans. It is not a mistake I will ever make again."
Stephenson is the second Chiefs starter who has been suspended by the league for at least one game. Wide receiver Dwayne Bowe was suspended for the Sept. 7 season opener against the Tennessee Titans for violation of the league's substance abuse policy stemming from his arrest last year for possession of marijuana. The charge was later dismissed.
"Obviously losing Donald is disappointing, but we are in full compliance with the league's policy," the Chiefs said in a statement.
The Chiefs' offensive line already was struggling before Stephenson's suspension was announced and did not play well in last week's preseason loss to the Carolina Panthers.
The leading candidates to replace Stephenson for the first four games are Ryan Harris and Jeff Linkenbach. Harris has played six NFL seasons with Denver and Houston with 39 career starts. He was signed by the Chiefs shortly before the start of training camp. Linkenbach was signed as a free agent in March after he played four seasons and made 27 starts for the Indianapolis Colts.