INDIANAPOLIS -- Indianapolis Colts running back Robert Turbin has been suspended four games for using performance-enhancing drugs, the league announced Friday.

He will be eligible to return October 1, ahead of the team's Week 5 game at New England on Oct. 4.

"A urine sample I provided to the NFL has resulted in a positive test of a banned substance under league policy with regards to Performance Enhancing Substances. It absolutely kills me that I allowed this to happen," Turbin wrote on Twitter. "It has always been a priority in my life to display a high level of leadership both on and off the field. I strive to be a person that people can look up to and strive to exemplify the definition of hard work.

"Unfortunately, I have made a mistake. A mistake that will not only have personal consequences, but will affect the Colts organization, an organization that I am extremely appreciative to be a part of. For that, I am truly sorry."

Turbin, who is entering his eighth season, spent the majority of the offseason program working with the first unit after the Colts decided not to re-sign veteran Frank Gore last winter and with Marlon Mack out with a shoulder injury.

Turbin played only six games last season because of an elbow injury.

The Colts, under new coach Frank Reich, will rely on Mack and rookies Nyheim Hines and Jordan Wilkins during Turbin's suspension. They also have Christine Michael and Josh Ferguson on the roster.