The team made the announcement on Saturday, shortly before the Cardinals had to reach their 53-man roster limit.
"In fairness to Matt, I think that it would be a tough position for him to be in a backup role," coach Ken Whisenhunt said. "Maybe a fresh start for him is what would be a good thing, for all of us."
The Cardinals tried to trade Leinart but found no acceptable deal. By cutting Leinart, Arizona doesn't have to pay him the $2.5 million he was due for the coming season, not to mention the $7.4 million, plus a $5.5 million roster bonus, he was scheduled to make next season.
Arizona thought it had a steal when Leinart, who led Southern California to two national championships and a third title game appearance, fell to the Cardinals at the No. 10 overall pick in 2006. Then-coach Dennis Green called it "a gift from heaven."
He started 11 games as a rookie under Green, then the first five the following season under new coach Ken Whisenhunt. But the big left-hander then went down with a broken collarbone and Kurt Warner took over.
Warner finished his career with two spectacular seasons, leading Arizona to consecutive NFC West titles, an incredible run to the Super Bowl and a 51-45 overtime victory over Green Bay in a playoff thriller last season.
Leinart mostly watched.
Even before Leinart was hurt, Warner was being used more and more. After the collarbone injury, Leinart started one game, at Tennessee last season when Warner was injured. This year, he expected to finally get his chance after Warner retired, but was replaced by Cleveland castoff Derek Anderson in the third preseason game.
"Do I feel like we didn't put him in a position to be successful?" Whisenhunt said. "I think that is open to debate. It has obviously been talked about a lot. I think that with every player on our team we are trying to give him the opportunity to succeed. I think we have always tried to be fair."
Leinart went public with his frustration on Monday, complaining he had outplayed Anderson and that his problems with Whisenhunt were "probably away from football."
That led to a meeting with Whisenhunt the following day. Although he was unhappy that Leinart took his issues public, Whisenhunt praised how the quarterback has handled things.
"The one thing I want to make very clear is how professional Matt was about the whole situation," the coach said. "I was very impressed with his conversation with me. He thanked the organization, the ownership, for all the time and effort that they had invested in him. He felt like he had gotten better and he had learned a lot and it meant a lot to me to hear him say that."
Leinart played two series in the final preseason game on Thursday night.
"This process was not about what some people said, two weeks into training camp or two preseason games," Whisenhunt said. "It's a complete body of work over a period of time. I will say like I have said before, Matt made tremendous progress. I was excited about what he had done, the work he had put in. I do believe that he is a better quarterback now then he was when I got here four years ago. It is not a slight on Matt, it was a decision that I felt gave us the best chance to win."
Leinart threw for 3,893 yards with 14 touchdowns and 20 interceptions with Arizona. Early on, he had to overcome his party boy image, which was enhanced when photos showed up on the Internet of him involving a hot tub, a "beer bong" and bikini-clad women.
Whisenhunt was on Leinart early about his work ethic, but said he was pleased with the quarterback's improvement in that area over his time with the Cardinals. Critics, though, pointed to Leinart's perceived lack of arm strength, apparent unwillingness to throw downfield and, perhaps most significantly, his failure to become a team leader.
The coach avoided any specific explanation about what Leinart's problems were.
"The most important thing to our players, our team and our fans is that we are in a position to win games," Whisenhunt said.
He noted how the players have rallied around Anderson.
"A lot of it is how his teammates respond to him and the confidence they have in him when he goes into the huddle," Whisenhunt said. "When he came out the other night and completed his first two passes on big plays, the guys rallied around him and that is what you like to see."
"Max has played consistently well throughout the preseason and practice," Whisenhunt said. "I understand the dynamic with regular season defenses and regular season games are different, but I am as comfortable as I can be with a rookie as our backup quarterback."
Anderson, who was released by the Cleveland Browns after Mike Holmgren took over as team president, signed with Arizona as a free-agent, initially to back up Leinart. The 6-foot-5 former Oregon State quarterback has a strong arm but has struggled at times with his accuracy. He made the Pro Bowl after leading the Browns to a 10-6 record in 2007 but lost his job to Brady Quinn last season.
Anderson said earlier this week that he was motivated to prove that the 2007 season was "no aberration, not a mirage."
Anderson had been claimed off waivers by Cleveland from Baltimore in 2005.
"He has grown in the little bit of time he has had with the first unit and in the practices," Whisenhunt said. "I like what I have seen. He has made progress. Part of how you assess Derek is we are judging him on what he has done with us."
The same could be said of Leinart.