Buffalo Bills running back CJ Spiller has insisted that he is fully focused on his team duties having returned to practice after a week off to deal with personal issues.

Spiller missed last week's training after his step-grandfather was accused of shooting four people in Lake Butler, killing two of them before turning the gun on himself.

Spiller thanked the team for their support during a difficult period and insists that he is now ready to turn his focus back to on-field matters.

"My running back group, Fred [Jackson] was the first one that knew. He came right up to me and he held his support. Coach [Tyrone] Wheatley was [also] up there talking to me and giving me support, just letting me have some moments to myself," Spiller told reporters.

"I understand that it is a tragic event that took place and it's going to take a while to cope with, but at the same time I can't forget the task and the goal and the dreams that we have here as a team and an organization.

"Once I touch the field, my main focus is football. That's how my whole family wanted it. That's how my mum wanted me to do. She told me when I come back to make sure my focus is on getting ready for New England."

The Bills will start the regular season at home to the New England Patriots on Sunday.