From the ever-reliable Wikipedia -
On August 19, 2013, Hopkins was named the Buffalo Bills starting placekicker over veteran placekicker, Rian Lindell.[5] On September 2, 2013, Hopkins was revealed to have sustained a groin injury. This prompted the Bills to sign Dan Carpenter. Due to a slow recovery from that injury and the need to further open roster spots, Hopkins was placed on the injured reserve list after Week 5.
Hopkins was given a chance to earn back his roster spot during the 2014 season, but lost the competition to Carpenter; the Bills released Hopkins on August 25, 2014.
The timing sucked because Hopkins is a stud with a big kickoff leg.