Robert Mathis of the Indianapolis Colts has been suspended without pay for the first four games of the 2014 regular season for violating the NFL policy on performance-enhancing substances.

Mathis will be eligible to return to the Colts' active roster on Monday, Sept. 29 following the team's September 28 game against the Tennessee Titans.

Mathis is eligible to participate in all offseason and preseason practices and games.

"We have learned that Robert Mathis will be required to serve a four game suspension under the League's policy on prohibited substances," a statement from the Colts read. "We recognize the extreme seriousness of this matter and will honor the confidentiality requirements of the League's program. We nevertheless wish to assure Robert and our fans that he remains an honored and cherished member of the Colts family and that we support him as he deals with this difficult challenge."