He managed just 13 points -- two after halftime -- on 4 for 17 shooting in the 102-91 loss to at Miami.
Anthony received treatment on Saturday at the team's practice facility before the Knicks left for South Beach.
Before going in for treatment, Anthony said he felt tightness in his shoulder, which was first hurt during Wednesday's game against the Brooklyn Nets.
He added that he was having trouble lifting his arm due to the tightness.
"It feels tight," he said. "It's hard to lift up; it's hard to do things."
Anthony reiterated that the injury impacted him throughout the Knicks' loss to Washington on Friday.
He had a season-high nine turnovers in the game and scored 10 points on 5-for-14 shooting. Anthony added five assists and eight rebounds.
"That wasn't me, that was out of character," he said.
The loss to Washington was a blow to the Knicks' playoff hopes as New York fell one game behind the Atlanta Hawks in the race for eighth place in the Eastern Conference.
The Knicks are now three games behind the Hawks in the loss column, though, and Atlanta holds the tiebreaker based on conference record.
"It's going to come down to the very end. Right now we have five games left and it's on us, it's on us," Anthony said.
X-rays taken on Anthony's shoulder late Friday night were negative, the Knicks said. The team called Anthony's injury a shoulder strain.
"That's where you get all of your strength from. Shooting, dribbling the ball, passing the ball," Anthony said.
Mike Woodson said before Sunday's game that Anthony told him that he was "OK" prior to tipoff.
Anthony suffered a labrum and rotator cuff tear in his left shoulder late last season and played through the injuries in the playoffs, though noted that there is no similarity between this injury and last year's ailment.
The 29-year-old Anthony has been the Knicks' most consistent performer this season. He's second in the NBA in per-game scoring (27.7) and is pulling down a career-high 8.2 rebounds per game.
But Anthony had his worst game of the season at the worst possible time for the Knicks (33-44).
The 10-year veteran had three turnovers in the final four minutes and let the ball slip out of his hands on the Knicks' final possession.
New York was down by one with 12.7 seconds to play. After Anthony lost the ball, it was batted toward J.R. Smith, who forced up an off-balance 3-pointer with two seconds to play.
Woodson said on Saturday that he hoped that Anthony, who plans to test free agency this summer, would pass the ball once Washington's defense collapsed on him on the Knicks' final possession.
"I wasn't looking for Melo to make the play to shoot the ball, I was looking for Melo to make the play to pass the ball," Woodson said. "It's the first game that I've seen him all season that he struggles, he struggled in terms of being able to handle the ball and make plays. That's not Carmelo. I haven't seen that all year."