"It's a time you take stuff for granted," the 29-year-old said. "It's a time you come to the realization that every game is precious."
Portis, who has played just 13 games the past two seasons because of a concussion in 2009 and a torn groin this year.
"You don't have forever and the last few years show you that," he said.
Portis, just 77 yards of 10,000 career rushing yards and 648 shy of Hall of Famer John Riggins' franchise record, wants to remain with the Redskins but doesn't know what to expect.
"That's out of my control," said Portis, who was averaging 4.2 yards per carry when he exited for good in Week 11, but is due to make $8.2 million in 2011. "That's up to the front office. If they want to keep me, of course they have first option. If they want me to let go, I'm OK with understanding the business side of this. It will be a bittersweet moment, but you gotta go on."
Washington wraps up its season when the Redskins host the New York Giants on Sunday.
Portis said that unlike many previous years, he worked diligently during the offseason to show new coach Mike Shanahan, who drafted him in Denver in 2002 and traded him to Washington in 2004, that he wanted to be part of the program.
Despite Shanahan's underwhelming 6-9 debut, Portis said the coach is turning around an organization that he believed was on the edge of disaster, notably by refusing to give into the demands of former All-Pro defensive lineman Albert Haynesworth. The Redskins had made Haynesworth the NFL's richest defensive player in 2009, before his much-publicized spats with Shanahan over his position and conditioning.
Portis said the Redskins lost a lot of close games in which a play or two by Haynesworth could have made a difference. "When you go and sacrifice a guy such as an Albert Haynesworth to prove like, 'OK. This is my team, I'm in control,' sacrifice a guy you know can help you win -- it's get with the program or get out," Portis said.
Ryan Torain, who's had his own injury issues but is four years younger than Portis and much cheaper, is emerging as Washington's No. 1 back, with 681 yards and 4.7 per carry. Not that Portis thinks he's done if Shanahan bids him adieu again.
"I know I got good football left in me, being fresh, the last two years not having a lot of contact," Portis said. "The two injuries, the concussion and the groin, was just really fluke injuries. I don't think that's a wear and tear like, 'Oh, his body broke down.' I don't think I'll be just a contributor on any team.
"I think a defensive coordinator will probably game plan (for me). I don't think you're gonna look and say, 'That's Portis. Don't worry 'bout him.'"