Both the Rams and national media reported Sam had gone unclaimed off waivers by other league teams before Sunday's 12 noon ET deadline passed.
The former University of Missouri standout now waits to see if any team will sign him to their practice squad, the likeliest route left for Sam to perhaps work his way into the NFL.
Sam, who had announced he was gay in February, failed to make the St. Louis Rams' 53-man roster for the 2014 regular season on Saturday, putting on hold his long cherished dream of playing in the league.
The 24-year-old was one of 22 players cut by the Rams and on Sunday he arrived at Rams Park to have his post-release interview with the team's head coach, Jeff Fisher.
Sam shook hands with a few reporters but declined to make any comment before speaking with Fisher.
The 6-feet-2 (1.88 m), 260-pound (118 kg) lineman became the first openly gay player to be selected in an NFL Draft when he was taken in the seventh round by the Rams in May.
Despite his success at Missouri, talent evaluators have said he might struggle in the NFL, perhaps too small to play regularly on the defensive line and not athletic enough to play in space as a linebacker.
Some believe he is unlikely to be re-signed by the Rams to their 10-player practice squad because their defensive line is such a strong unit.
The co-defensive player of the year in the Southeastern Conference had been vying with the undrafted Ethan Westbrooks for the last of nine defensive line spots with the Rams.
Westbrooks had made the roster on Saturday after displaying greater energy and big-play potential than his rival.
"Mike's got ability. Mike played well," Fisher told reporters on Saturday, having described Sam's release as simply "a football decision".
"He has the ability to play some place," the coach said. "It's gotta be the right place, it's gotta be a fit....
"He's a much better player now than he was when he got here."
There is currently only one openly gay player in North America's four major professional sports leagues, basketball's Jason Collins, who joined the NBA's Brooklyn Nets last season.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Gene Cherry)