Casillas, 30, originally signed on with the Saints as an undrafted free agent out of Wisconsin back in 2009. He spent three years in New Orleans before catching on with the Buccaneers and Patriots.
The Giants signed him to a contract in 2015. Casillas is in the final year of his three-year, $8 million contract and stands to make a base salary of $2.25 million for the 2017 season.
In 2017, Casillas appeared in eight games for the Giants and recorded 35 tackles, no sacks or interceptions, and a pass defense.