Garnett, 25, is a former first-round pick by the 49ers in the 2016 NFL Draft. He was entering the second year of a four year $9.304 million rookie contract when the 49ers waived him coming out of the preseason.
Garnett had been working his way back from an offseason knee scope.
In 2018, Garnett appeared in 7 games for the 49ers.
Johnson, 28, is a former fifth-round pick of the Steelers back in 2014. He lasted just a few months in Pittsburgh before he was waived and later claimed by the Jets.
Johnson had brief stints with the Lions and Dolphins before the 49ers signed him to a contract this past May. Unfortunately, he wound up being among their roster cuts coming out of the preseason.
In 2010, Johnson appeared in 10 games for the Dolphins.
Green, 27, is a former third-round pick of the Cowboys back in 2015. He was in the final year of his four-year, $2.951 million contract when the Cowboys waived him coming out of the preseason last year.
Green later had brief stints with the Saints and Raiders before the Broncos signed him to a contract a few months ago. Unfortunately, he released at the start of the regular season.
In 2018, Green appeared in four games for the Raiders.