These two moves will account for $13.5 million in salary-cap space for the Bears in 2020.
Gabriel, 29, had 29 receptions for 353 yards and four touchdowns for the Bears last season.
Amukamara, 30, spent three seasons with the Bears. A first-round draft pick of the New York Giants in 2011, he was part of Super Bowl team there in his rookie year.
After a stint with the Jacksonville Jaguars in 2016, he signed with the Bears in 2017. In March 2018, he signed a three-year, $27 million extension.