Edward Lewis of NFL.com passed along comments Bush made about the decision during an appearance on NFL Network's NFL Total Access.
"I'm done," he said. "Yeah, I'm done. I said it. It's not breaking news. I've been saying it. I said it all season long. I said, 'Listen, if I don't play this year, I'm going to retire.' Because I'm not going to spend a whole year off, come back, 33 years old, trying to get back into the league. Listen, once you get to a certain age as a running back, they just start to slowly weed you out."
Bush suffered a season-ending knee injury when he slipped on concrete during a game in St. Louis in November 2015. Michael Rothstein of ESPN.com relayed what the USC product said in February 2016 about his desire to continue playing after the career-altering setback.
"I'm not retiring," Bush said. "I'm still playing. No, I'm not done. And I would never—knock on wood—I never want to end my career like that, going out with that."
Though he received an opportunity with the Buffalo Bills during the 2016 season, he was no longer the big-play asset he was earlier in his career. That led to his minuscule role despite the team's heavy reliance on the running game, which signaled the end was near.
The 32-year-old California native rose to stardom early. He was a 5-star high school prospect who rated as the No. 17 overall player in the 2003 college recruiting class, according to 247Sports.
He proceeded to shine across three years at USC. The dynamic back racked up 4,470 yards and 38 touchdowns from scrimmage while adding four more scores on special teams. He even had a passing TD for the Trojans.
Bush received numerous accolades during that run of success and won the Heisman Trophy in 2005. He was, however, forced to give up the top individual honor in college football, and USC was stripped of its 2004 national title, because of an improper benefits scandal.
Nevertheless, having emerged as an electrifying offensive weapon in high school and having put those skills on full display in college, he became the second overall pick of the New Orleans Saints in 2006.
There were moments during his pro career that reminded fans of those glory days with the Trojans, but his game never fully translated to the highest level. He rushed for more than 1,000 yards just twice in stints with the Saints, Bills, Miami Dolphins, Detroit Lions and San Francisco 49ers.
Injuries were a factor for the undersize (6'0", 205 pounds) rusher, who appeared in all 16 regular-season games only twice in his 11 NFL seasons.
The dual-threat star tallied 9,088 yards from scrimmage and 54 touchdowns. He added four more touchdowns as one of the league's most dangerous punt returners during his first handful of years. He was also part of the Saints team that won Super Bowl XLIV.
But Bush's time in the NFL ended with a whimper. Though he might not have made the franchise-changing impact that was expected when he was drafted, he was a valuable asset for most of his time in the league.
All the ailments over the years took a toll, however, as he lacked explosiveness during the past few seasons.