McCoy, 31, ran for a career-low 514 yards in 2018, sparking outside conversation about whether the two-time All-Pro could still be productive. He has played 10 years in the league and his 10,606 yards rushing rank 25th on the career list and fourth among active players.
McCoy was entering the final year of a five-year contract he signed after his acquisition in a trade with Philadelphia, where he led the NFL in rushing yards in 2013.
McCoy had an inconsistent four seasons with the Bills. He struggled in his first year, finishing with 895 yards rushing. McCoy attributed that to being unfocused as a result of being traded. McCoy responded by topping 1,100 yards rushing in each of his next two seasons. But he struggled last year when he finished with a career-worst 752 yards from scrimmage.
Gore, 36, was still effective in 2018, recording the fifth-highest yards-per-carry mark (4.6) of his 14-year career, albeit on his second-fewest attempts per game. He has been remarkably healthy, playing in 210 of 224 possible regular-season games.
Singletary, the team's 2019 third-round pick, was a prolific runner in three seasons at Florida Atlantic, rushing for 4,287 yards and 66 touchdowns. He also caught 51 passes, 26 of which came during his freshman season.
Beane said the decision to release McCoy came at "the last minute" but became a more realistic option as Singletary developed during the preseason.
Beane confirmed he explored the idea of trading McCoy once he made the decision to release him, but ultimately never received -- or sent -- an official offer.
"We did look around to see if there was a right fit but we didn't find one," Beane said. "This kind of gives him a chance to choose his destination, as well, and he's earned that."
Buffalo was prepared to operate with a "running back by committee" approach during the 2019 season and factored McCoy's potential response into the decision to part ways with him, according to a source.
McCoy was reportedly not expecting the news and Beane said the running back was "frustrated" by his release. A source told ESPN that the Bills value the relationship between Singletary and Gore and felt comfortable with the rookie learning from Gore without McCoy.
Information from ESPN's Marcel Louis-Jacques and The Associated Press was used in this report.