BUFFALO, N.Y. -- Buffalo Bills linebacker A.J. Tarpley cites two concussions he sustained last year as the reason he has elected to retire from football after just one season.

Tarpley's agent, Ryan Downey, confirmed his client's decision on Thursday, a day after Tarpley announced the news on his Instagram account.

Tarpley called it "the hardest" decision and one that came following months of introspection after sustaining what he referred to as the third and fourth concussions of his playing career last season. He wrote: "I am walking away from the game I love to preserve my future health."

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Downey said Tarpley reached his decision after visiting the Bills headquarters and meeting with officials within the past week.

Tarpley signed with Buffalo as an undrafted rookie free agent out of Stanford. He had a sack and two interceptions in 15 games -- including two starts -- last season.