Running back Fred Jackson had his season end when he was placed on the injured reserve list by the Buffalo Bills on Tuesday with a leg injury, the team announced. Jackson was injured in the fourth quarter of the Bills' 15-12 home loss to the St. Louis Rams on Sunday when he was tackled by two defenders. Jackson missed two games earlier this year with a sprained right knee. The Bills promoted defensive tackle Jay Ross from the practice squad to take Jackson's place on 53-man roster. An undrafted free agent in 2010, Ross has spent the past two seasons on Buffalo's practice squad. Also, the Bills signed running back Zach Brown to a practice squad contract. The Pitt product was cut by Buffalo after training camp.