Knuble, who will become an unrestricted free agent on July 1, said Capitals GM George McPhee had informed him that the team would not be re-signing him.
On Wednesday, Knuble posted a farewell message to Capitals fans on his personal Twitter account: "To Caps fans everywhere: thanks for an awesome 3 yrs in DC. We loved living and playing here. Great teammates, great friends. We'll miss it"
Knuble had just six goals and 12 assists in 72 regular-season games, but found himself skating on the fourth line and an occasional healthy scratch. It snapped an eight-season string of 20-goal seasons.
He also had just three points in the playoffs while playing in 11 of the Caps' 14 games.
Knuble, who will turn 40 on July 4, said he wasn't surprised by what McPhee told him.
"I don't think it was unexpected, the way things went this season," Knuble told the newspaper. "There are younger guys stepping up and those guys will need a spot to play and a chance to play. … It's really the first time in my career that I've been told by a team they don't want me back, but it's not like I was blindsided."
In three seasons with the Capitals, Knuble had 59 goals and 52 assists in 220 regular-season games, most of them spent as a top-six forward. He also was a well-respected leader in the locker room.
Knuble played in his 1,000th NHL game last season, and in 15 seasons with the Red Wings, Rangers, Bruins, Flyers and Capitals, he has 274 goals and 540 points. A 1991 fourth-round pick of the Red Wings, he didn't emerge as a top-flight player until the 2002-03, when he already was 30 years old. An injury to Sergei Samsonov allowed Knuble to move to the Bruins' top line alongside Joe Thornton and Glen Murray, and Knuble responded with a 30-goal season. He averaged 27 goals a season from 2002-03 until 2010-11.
Knuble said he feels healthy and would like to continue playing, but understands the realities of his situation.
"I was thinking the other day that my body feels as good as it did when I came into the League," Knuble said. "At this stage of my career, you understand that nobody's going to make long-term plans with you or give you a long-term commitment, but I feel I can contribute. People look at me being 39 years old, but I just view my age as a number. Physically, I feel good and I think I relate to my teammates very well.
"I feel prepared for anything. I could be in hockey, outside of hockey -- but my first priority would be to keep playing."