He sat out the Rams ' first exhibition against the Dallas Cowboys because of a hamstring issue .
Gaines started 15 games as a rookie in 2014 but was sidelined all of last season because of a foot injury suffered during training camp .
Gaines sat out the Rams ' first exhibition against the Dallas Cowboys because of a hamstring issue .
Gaines started 15 games as a rookie in 2014 but was sidelined all of last season because of a foot injury suffered during training camp .