Walker (undisclosed) was waived/injured by the Jets on Tuesday, per the NFL's official transaction log.
Walker was claimed off waiver by the Jets in May and was working as a depth tailback in camp. He appeared in four games for the 49ers last season, rushing once for three yards and catching one pass for 27 yards. The 25-year-old will revert to New York's injured reserve if he goes through waivers unclaimed.