BOSTON — Patriots defensive end Rob Ninkovich uncharacteristically missed the first day of training camp. Then he missed the second day. And the third. After New England officials announced a mystery news conference for the next morning, most had guessed the reason: The Patriots most versatile defensive player of the past eight seasons had decided to retire.

“After many months trying to get ready for another season, I know the toll it takes,” Ninkovich said Sunday. “Everything I worked for is just through hard work, dedication, perseverance, and overcoming adversity.  It wasn’t an easy decision. But after 11 (NFL) seasons and 19 years playing football, it’s time for me to walk away. I look forward to the next phase of my life.”

Many Patriots’ players and coaches attended the announcement, including quarterback Tom Brady and head coach Bill Belichick.

The room was so packed with players, coaches and media members that Belichick had to sit on the floor to witness one of his most important players hang up his cleats.

“It’s with really mixed emotions that I stand here today to congratulate Rob [Ninkovich] on just a tremendous, tremendous football and personal career and his personal contributions to the Patriots at the same time,” Belichick said before Ninkovich arrived to the podium. “Rob is one of the most unselfish players I’ve ever coached. Congratulations on a tremendous career. It’s been an honor to coach you. Thank you for your contributions to the Patriots and to me personally. Thank you.”

Ninkovich’s career began in 2006, when he was drafted in the fifth round by the New Orleans Saints. A serious knee injury nearly derailed his career, but he bounced back and forth between the Saints and Miami Dolphins, getting cut four times before making his way onto the Patriots training camp roster in 2009. He was the last player added before camp.

“This was my only chance,” Ninkovich said. “I had to turn heads. I had to go against (All-Pro tackle) Matt Light. First rep I beat him. Second rep I bet him. Third rep I beat him. That was the start of taking advantage of an opportunity.”

Ninkovich became a stalwart on the Patriots’ front seven, spending time at both defensive end and linebacker in both three-man and four-man defensive fronts, exemplifying his versatility.

Since 2009, Ninkovich is one of just two players, Julius Peppers being the other, to garner at least 35 sacks, nine forced fumbles, 10 fumble recoveries and five interceptions.

As the announcement came to a close, Ninkovich got teary-eyed when he looked at Belichick, sitting on the floor.

“I gave you everything I had, coach. I hope it was enough.”