NFL commissioner Roger Goodell upheld Tom Brady's four-game suspension Tuesday, setting up a legal battle between the league and one of its biggest stars.

Less than 24 hours before Brady was set to report for the first day of training camp, Goodell denied the Patriots quarterback's appeal of the suspension for illegally tampering with footballs used in last season's AFC Championship Game.

At the heart of Goodell's decision was the bombshell disclosure that Brady directed that the cellphone he had used for the previous four months leading up to the championship game against the Colts be destroyed by his assistant.

See alsoRead NFL's decision on Tom Brady's appeal

"Notwithstanding my enormous respect for his accomplishments on the field and for his contributions and role in the community, I find that, with respect to the game balls used in the AFC Championship Game and the subsequent investigation, Mr. Brady engaged in conduct detrimental to the integrity of, and public confidence in, the game of professional football," Goodell wrote at the conclusion of his 20-page decision. "The four-game suspension is confirmed."

The NFL Players Association, which represented Brady in his June 23 appeal, released a statement saying it will "appeal this outrageous decision."

That appeal likely would come in federal court.

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The NFL Management Council, which represents member clubs in the league, filed a complaint against the NFLPA in U.S. District Court-Southern District of New York on Tuesday asking the court to confirm Goodell's authority to discipline players.

Calling it important new information disclosed by Brady and his representatives, Goodell wrote that Brady directed that the cellphone be destroyed shortly before he met with NFL-appointed investigator Ted Wells on March 6.

"[Brady] did so even though he was aware that the investigators had requested access to text messages and other electronic information that had been stored on that phone," the NFL said in a statement accompanying Goodell's decision. "During the four months that the cellphone was in use, Brady had exchanged nearly 10,000 text messages, none of which can now be retrieved from that device."

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Goodell noted that the NFL was not made aware of the fact that the phone was destroyed until June 18, nearly four months after the quarterback was first told that investigators wanted to examine the phone and its text messages.

"The commissioner found that Brady's deliberate destruction of potentially relevant evidence went beyond a mere failure to cooperate in the investigation and supported a finding that he had sought to hide evidence of his own participation in the underlying scheme to alter the footballs," the NFL said in its statement.

Goodell said Brady had the phone destroyed on or about March 6, the date that he was to meet with Wells, and that he started using a new phone at that time. Brady had testified that it was normal to have his cellphones destroyed when he began using a new phone. Goodell, however, noted that the phone Brady had used before the one in use that included texts that NFL investigators wanted to see was still available.

The Patriots expressed disappointment in Goodell's decision and offered strong support for Brady.

"Most would agree that the penalties levied originally were excessive and unprecedented, especially in light of the fact that the league has no hard evidence of wrongdoing," the team said in a statement. "We continue to unequivocally believe in and support Tom Brady."

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Brady's agent, Don Yee, said Goodell's decision is "deeply disappointing, but not surprising because the appeal process was thoroughly lacking in procedural fairness. Most importantly, neither Tom nor the Patriots did anything wrong. And the NFL has no evidence that anything inappropriate occurred. The appeal process was a sham, resulting in the commissioner rubber-stamping his own decision."

Brady was suspended for four games on May 11, five days after a 243-page report by Wells concluded that it was "more probable than not" that the Patriots deliberately underinflated the footballs used in the first half of the conference championship game. The report also said that Brady was at least "generally aware" that the footballs were underinflated.

"Based on the Wells Report and the evidence presented at the hearing, commissioner Goodell concluded in his decision that Brady was aware of, and took steps to support, the actions of other team employees to deflate game footballs below the levels called for by the NFL's official playing rules," the NFL said in its statement.

Wells' report produced evidence that the attorney claims showed how Patriots locker room attendants Jim McNally and John Jastremski were keeping the footballs below the 12.5 PSI minimum prescribed by NFL rules. Both McNally and Jastremski were suspended without pay by the Patriots shortly after the Wells report came out.

Goodell noted in his report that the league believed it would be beneficial for McNally and Jastremski to testify at Brady's appeal in June. But Brady's NFLPA counsel declined to make them available.

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In addition to Brady's suspension, the Patriots were fined $1 million and have been ordered to forfeit a first-round draft pick in 2016 and a fourth-round selection in 2017. Patriots owner Robert Kraft announced at the NFL's spring meeting in May that the team would not challenge the sanctions imposed by the league.