Anthony has been dealing with soreness in his left knee since the second game of the season.
His availability for each game depends on how his knee feels prior to tipoff. He has missed four games due to the knee discomfort.
"Tonight it feels like fatigue, and not getting a chance to recover from last night," Anthony said. "I felt this before the game, but I looked around the locker room and we have seven or eight guys ready to go -- I really didn't have a choice but to go out there and attempt to play and see how much I could take."
Anthony played 19 minutes Sunday, scoring 13 points and pulling down five rebounds. He was playing his second game in two nights.
On Friday, Anthony played 46 minutes in a road loss to the Sacramento Kings.
Anthony had 36 points in the 135-129 overtime loss.
On Sunday, Anthony appeared to aggravate his knee injury on a drive in the second quarter against Portland.
Knicks coach Derek Fisher was asked about sitting Anthony for an extended period to address the sore knee.
"Carmelo is Carmelo. We don't necessarily make decisions for him," Fisher said. "He's part of the conversation. So we have opinions that we've expressed to him. We talk about different things, but really it is a decision that he has to also want to make for himself and his career. He's also conferenced about the team and his teammates, and so we'll continue to find a right balance of it all."
Anthony said earlier this month that close friends have suggested that he take himself out of the lineup for an extended period to rest his knee.
Anthony has resisted that approach thus far. He also is hoping to avoid surgery to repair the injury, calling the option a "last" resort earlier this month.
Anthony, in the first year of a five-year, $124 million contract, has been told by the team's medical staff that he is not at risk of further injury if he chooses to continue to play. But the team's staff has also told him that the injury will not improve if he continues to play.
Anthony is one of several injured Knicks.
The injuries have taken a toll on New York.
At 5-27, the Knicks are off to the worst 32-game start in franchise history and have lost 17 of 18 games.
Information from The Associated Press was used in this report.