Los Angeles Chargers star defensive end Joey Bosa already was ruled out for Sunday's game against the Buffalo Bills because of a bruised bone in his left foot, and his injury now is expected to sideline him into October, sources told ESPN.

The injury is expected to keep Bosa out longer than the initial timeline of couple of weeks, according to sources.

Bosa is rehabbing his foot, with the hope that the swelling goes down and the foot stabilizes. But if it doesn't, surgery would not be ruled out.

He suffered the initial injury, described as a sore foot by Chargers coach Anthony Lynn, on Aug. 7 during 11-on-11 team drills in practice. Bosa did not participate in any preseason games, but the Chargers considered the injury minor and expected him to be ready by the start of the regular season.

The No. 3 selection in the 2016 draft, Bosa led the Chargers in sacks last season with 12.5 as part of the team's talented pass-rushing tandem alongside Melvin Ingram, who had 10.5 sacks in 2017.

ESPN's Eric D. Williams contributed to this report.