NFL: Key Chiefs blocker Stephenson gets four-game ban

Kansas City Chiefs starting right tackle Donald Stephenson was suspended Friday by the National Football League for the first four games of the upcoming season for a performance-enhancing substances violation.

Stephenson, who has not missed a game for the Chiefs since being taken by the club in the third round of the 2012 NFL Draft, blamed his lack of a theraputic-use exemption for the violation without revealing the substance involved.

"I'm extremely sorry that I failed to check with the NFL, NFL Players Association or Chiefs medical team before I took a medication that requires a therapeutic use exemption," Stephenson said in an apology statement released by the players' union.

"It is not a mistake I will ever make again. I will train extremely hard during my time away from the team and I will be ready to contribute to my team's effort to win a Super Bowl as soon as I return."

Stephenson, who can take part in pre-season practices and games, will be able to return to the Chiefs on September 30, the day after they host New England. He will also miss the team's September 7 opener against Tennessee and games at Denver and Miami.

"Obviously losing Donald is disappointing but we are in full compliance with the league's policy," the Chiefs said in a statement.